diff --git a/src/Swarm/TUI/Controller.hs b/src/Swarm/TUI/Controller.hs
index eaa1e775c2..71a62a0250 100644
--- a/src/Swarm/TUI/Controller.hs
+++ b/src/Swarm/TUI/Controller.hs
@@ -1,5 +1,4 @@
 {-# LANGUAGE OverloadedStrings #-}
-{-# LANGUAGE PatternSynonyms #-}
 
 -- |
 -- Module      :  Swarm.TUI.Controller
@@ -80,33 +79,18 @@ import Swarm.Language.Requirement qualified as R
 import Swarm.Language.Syntax
 import Swarm.Language.Typed (Typed (..))
 import Swarm.Language.Types
+import Swarm.TUI.Controller.ControllerUtils
+import Swarm.TUI.Editor.EditorController qualified as EC
+import Swarm.TUI.Editor.Util qualified as EU
 import Swarm.TUI.Inventory.Sorting (cycleSortDirection, cycleSortOrder)
 import Swarm.TUI.List
 import Swarm.TUI.Model
-import Swarm.TUI.View (generateModal)
+import Swarm.TUI.View.ViewUtils (generateModal)
 import Swarm.Util hiding ((<<.=))
 import Swarm.Version (NewReleaseFailure (..))
 import System.Clock
 import Witch (into)
 
--- | Pattern synonyms to simplify brick event handler
-pattern Key :: V.Key -> BrickEvent n e
-pattern Key k = VtyEvent (V.EvKey k [])
-
-pattern CharKey, ControlChar, MetaChar :: Char -> BrickEvent n e
-pattern CharKey c = VtyEvent (V.EvKey (V.KChar c) [])
-pattern ControlChar c = VtyEvent (V.EvKey (V.KChar c) [V.MCtrl])
-pattern MetaChar c = VtyEvent (V.EvKey (V.KChar c) [V.MMeta])
-
-pattern ShiftKey :: V.Key -> BrickEvent n e
-pattern ShiftKey k = VtyEvent (V.EvKey k [V.MShift])
-
-pattern EscapeKey :: BrickEvent n e
-pattern EscapeKey = VtyEvent (V.EvKey V.KEsc [])
-
-pattern FKey :: Int -> BrickEvent n e
-pattern FKey c = VtyEvent (V.EvKey (V.KFun c) [])
-
 -- | The top-level event handler for the TUI.
 handleEvent :: BrickEvent Name AppEvent -> EventM Name AppState ()
 handleEvent = \case
@@ -288,20 +272,74 @@ handleMainEvent ev = do
     VtyEvent vev
       | isJust (s ^. uiState . uiModal) -> handleModalEvent vev
     -- toggle creative mode if in "cheat mode"
+
+    MouseDown (TerrainListItem pos) V.BLeft _ _ ->
+      uiState . uiWorldEditor . terrainList %= BL.listMoveTo pos
     ControlChar 'v'
       | s ^. uiState . uiCheatMode -> gameState . creativeMode %= not
+    -- toggle world editor mode if in "cheat mode"
+    ControlChar 'e'
+      | s ^. uiState . uiCheatMode ->
+        uiState . uiWorldEditor . isWorldEditorEnabled %= not
+    MouseDown n V.BRight _ mouseLoc -> do
+      let worldEditor = s ^. uiState . uiWorldEditor
+      case (n, worldEditor ^. isWorldEditorEnabled) of
+        -- "Eye Dropper" tool:
+        (WorldPanel, True) -> do
+          mouseCoordsM <- Brick.zoom gameState $ mouseLocToWorldCoords mouseLoc
+          case mouseCoordsM of
+            Nothing -> return ()
+            Just coords -> uiState . uiWorldEditor . terrainList %= BL.listMoveToElement newVal
+             where
+              newVal = EU.getTerrainAt worldEditor (s ^. gameState . world) coords
+        _ -> continueWithoutRedraw
+    MouseDown n V.BLeft [V.MCtrl] mouseLoc ->
+      case n of
+        WorldPanel -> do
+          worldEditor <- use $ uiState . uiWorldEditor
+          when (worldEditor ^. isWorldEditorEnabled) $ do
+            let maybeTerrainType = fmap snd $ BL.listSelectedElement $ worldEditor ^. terrainList
+            case maybeTerrainType of
+              -- TODO: Use a MaybeT monad transformer?
+              Nothing -> return ()
+              Just terrain -> do
+                mouseCoordsM <- Brick.zoom gameState $ mouseLocToWorldCoords mouseLoc
+                case mouseCoordsM of
+                  Nothing -> return ()
+                  Just mouseCoords -> do
+                    uiState . uiWorldEditor . paintedTerrain %= M.insert mouseCoords terrain
+        -- TODO: Screen updates are laggy, and the needsRedraw flag doesn't seem to help
+        _ -> return ()
     MouseDown n _ _ mouseLoc ->
       case n of
         WorldPanel -> do
-          mouseCoordsM <- Brick.zoom gameState (mouseLocToWorldCoords mouseLoc)
-          uiState . uiWorldCursor .= mouseCoordsM
+          mouseCoordsM <- Brick.zoom gameState $ mouseLocToWorldCoords mouseLoc
+          case mouseCoordsM of
+            Nothing -> uiState . uiWorldCursor .= mouseCoordsM
+            Just mouseCoords -> do
+              selectorStage <- use $ uiState . uiWorldEditor . boundsSelectionStep
+              -- We swap the horizontal and vertical coordinate, and invert the vertical cooridnate.
+              -- TODO What is mouseLocToWorldCoords??
+              let toWorldCoords (W.Coords (mx, my)) = W.Coords (my, -mx)
+              case selectorStage of
+                UpperLeftPending -> uiState . uiWorldEditor . boundsSelectionStep .= LowerRightPending mouseCoords
+                -- TODO: Validate that the lower-right click is below and to the right of the top-left coord
+                LowerRightPending upperLeftMouseCoords -> do
+                  uiState . uiWorldEditor . editingBounds
+                    .= Just (toWorldCoords upperLeftMouseCoords, toWorldCoords mouseCoords)
+                  uiState . uiWorldEditor . boundsSelectionStep .= SelectionComplete
+                  setFocus WorldEditorPanel
+                SelectionComplete -> uiState . uiWorldCursor .= mouseCoordsM
         REPLInput -> do
-          setFocus REPLPanel
+          setFocus REPLPanel -- TODO: Is this redundant???
           handleREPLEvent ev
         _ -> continueWithoutRedraw
     MouseUp n _ _mouseLoc -> do
       case n of
         InventoryListItem pos -> uiState . uiInventory . traverse . _2 %= BL.listMoveTo pos
+        x@(WorldEditorPanelControl y) -> do
+          uiState . uiWorldEditor . editorFocusRing %= focusSetCurrent x
+          EC.activateWorldEditorFunction y
         _ -> return ()
       setFocus $ case n of
         -- Adapt click event origin to their right panel.
@@ -311,6 +349,7 @@ handleMainEvent ev = do
         InventoryList -> RobotPanel
         InventoryListItem _ -> RobotPanel
         InfoViewport -> InfoPanel
+        WorldEditorPanelControl _ -> WorldEditorPanel
         _ -> n
     -- dispatch any other events to the focused panel handler
     _ev -> do
@@ -318,6 +357,7 @@ handleMainEvent ev = do
       case focusGetCurrent fring of
         Just REPLPanel -> handleREPLEvent ev
         Just WorldPanel -> handleWorldEvent ev
+        Just WorldEditorPanel -> EC.handleWorldEditorPanelEvent ev
         Just RobotPanel -> handleRobotPanelEvent ev
         Just InfoPanel -> handleInfoPanelEvent infoScroll ev
         _ -> continueWithoutRedraw
@@ -363,21 +403,8 @@ toggleModal :: ModalType -> EventM Name AppState ()
 toggleModal mt = do
   modal <- use $ uiState . uiModal
   case modal of
-    Nothing -> do
-      newModal <- gets $ flip generateModal mt
-      ensurePause
-      uiState . uiModal ?= newModal
+    Nothing -> openModal mt
     Just _ -> uiState . uiModal .= Nothing >> safeAutoUnpause
- where
-  -- Set the game to AutoPause if needed
-  ensurePause = do
-    pause <- use $ gameState . paused
-    unless (pause || isRunningModal mt) $ do
-      gameState . runStatus .= AutoPause
-
--- | The running modals do not autopause the game.
-isRunningModal :: ModalType -> Bool
-isRunningModal mt = mt `elem` [RobotsModal, MessagesModal]
 
 handleModalEvent :: V.Event -> EventM Name AppState ()
 handleModalEvent = \case
@@ -394,6 +421,10 @@ handleModalEvent = \case
     Brick.zoom (uiState . uiModal . _Just . modalDialog) (handleDialogEvent ev)
     modal <- preuse $ uiState . uiModal . _Just . modalType
     case modal of
+      Just TerrainPaletteModal -> do
+        listWidget <- use $ uiState . uiWorldEditor . terrainList
+        newList <- nestEventM' listWidget $ BL.handleListEvent ev
+        uiState . uiWorldEditor . terrainList .= newList
       Just _ -> handleInfoPanelEvent modalScroll (VtyEvent ev)
       _ -> return ()
 
diff --git a/src/Swarm/TUI/Controller/ControllerUtils.hs b/src/Swarm/TUI/Controller/ControllerUtils.hs
new file mode 100644
index 0000000000..b730c7f2da
--- /dev/null
+++ b/src/Swarm/TUI/Controller/ControllerUtils.hs
@@ -0,0 +1,45 @@
+{-# LANGUAGE PatternSynonyms #-}
+
+module Swarm.TUI.Controller.ControllerUtils where
+
+import Brick hiding (Direction)
+import Control.Lens
+import Control.Monad (unless)
+import Graphics.Vty qualified as V
+import Swarm.Game.State
+import Swarm.TUI.Model
+import Swarm.TUI.View.ViewUtils (generateModal)
+
+-- | Pattern synonyms to simplify brick event handler
+pattern Key :: V.Key -> BrickEvent n e
+pattern Key k = VtyEvent (V.EvKey k [])
+
+pattern CharKey, ControlChar, MetaChar :: Char -> BrickEvent n e
+pattern CharKey c = VtyEvent (V.EvKey (V.KChar c) [])
+pattern ControlChar c = VtyEvent (V.EvKey (V.KChar c) [V.MCtrl])
+pattern MetaChar c = VtyEvent (V.EvKey (V.KChar c) [V.MMeta])
+
+pattern ShiftKey :: V.Key -> BrickEvent n e
+pattern ShiftKey k = VtyEvent (V.EvKey k [V.MShift])
+
+pattern EscapeKey :: BrickEvent n e
+pattern EscapeKey = VtyEvent (V.EvKey V.KEsc [])
+
+pattern FKey :: Int -> BrickEvent n e
+pattern FKey c = VtyEvent (V.EvKey (V.KFun c) [])
+
+openModal :: ModalType -> EventM Name AppState ()
+openModal mt = do
+  newModal <- gets $ flip generateModal mt
+  ensurePause
+  uiState . uiModal ?= newModal
+ where
+  -- Set the game to AutoPause if needed
+  ensurePause = do
+    pause <- use $ gameState . paused
+    unless (pause || isRunningModal mt) $ do
+      gameState . runStatus .= AutoPause
+
+-- | The running modals do not autopause the game.
+isRunningModal :: ModalType -> Bool
+isRunningModal mt = mt `elem` [RobotsModal, MessagesModal]
diff --git a/src/Swarm/TUI/Editor/EditorController.hs b/src/Swarm/TUI/Editor/EditorController.hs
new file mode 100644
index 0000000000..7980aadf02
--- /dev/null
+++ b/src/Swarm/TUI/Editor/EditorController.hs
@@ -0,0 +1,46 @@
+module Swarm.TUI.Editor.EditorController where
+
+import Brick hiding (Direction)
+import Brick.Focus
+import Control.Lens
+import Control.Monad.IO.Class (liftIO)
+import Graphics.Vty qualified as V
+import Swarm.Game.State
+import Swarm.TUI.Controller.ControllerUtils
+import Swarm.TUI.Editor.Util qualified as EU
+import Swarm.TUI.Model
+
+------------------------------------------------------------
+-- World Editor panel events
+------------------------------------------------------------
+
+activateWorldEditorFunction :: WorldEditorFocusable -> EventM Name AppState ()
+activateWorldEditorFunction BrushSelector = openModal TerrainPaletteModal
+activateWorldEditorFunction EntitySelector =
+  liftIO $ putStrLn "TODO"
+activateWorldEditorFunction AreaSelector = do
+  selectorStage <- use $ uiState . uiWorldEditor . boundsSelectionStep
+  case selectorStage of
+    SelectionComplete -> uiState . uiWorldEditor . boundsSelectionStep .= UpperLeftPending
+    _ -> return ()
+activateWorldEditorFunction OutputPathSelector =
+  liftIO $ putStrLn "File selection"
+
+-- | Handle user input events in the robot panel.
+handleWorldEditorPanelEvent :: BrickEvent Name AppEvent -> EventM Name AppState ()
+handleWorldEditorPanelEvent = \case
+  Key V.KEsc -> uiState . uiWorldEditor . boundsSelectionStep .= SelectionComplete
+  Key V.KEnter -> do
+    fring <- use $ uiState . uiWorldEditor . editorFocusRing
+    case focusGetCurrent fring of
+      Just (WorldEditorPanelControl x) -> activateWorldEditorFunction x
+      _ -> return ()
+  ControlChar 's' -> do
+    worldEditor <- use $ uiState . uiWorldEditor
+    let fp = worldEditor ^. outputFilePath
+    maybeBounds <- use $ uiState . uiWorldEditor . editingBounds
+    w <- use $ gameState . world
+    liftIO $ writeFile fp $ EU.getEditedMapAsString worldEditor maybeBounds w
+  CharKey '\t' -> uiState . uiWorldEditor . editorFocusRing %= focusNext
+  Key V.KBackTab -> uiState . uiWorldEditor . editorFocusRing %= focusPrev
+  _ -> return ()
diff --git a/src/Swarm/TUI/Editor/EditorView.hs b/src/Swarm/TUI/Editor/EditorView.hs
new file mode 100644
index 0000000000..f300c17d08
--- /dev/null
+++ b/src/Swarm/TUI/Editor/EditorView.hs
@@ -0,0 +1,95 @@
+module Swarm.TUI.Editor.EditorView where
+
+import Brick hiding (Direction)
+import Brick.Focus
+import Brick.Widgets.List qualified as BL
+import Control.Lens hiding (Const, from)
+import Data.List qualified as L
+import Swarm.Game.World qualified as W
+import Swarm.TUI.Attr
+import Swarm.TUI.Border
+import Swarm.TUI.Model
+import Swarm.TUI.Panel
+
+import Swarm.TUI.View.ViewUtils
+
+drawWorldEditor :: FocusRing Name -> UIState -> Widget Name
+drawWorldEditor toplevelFocusRing uis =
+  if worldEditor ^. isWorldEditorEnabled
+    then
+      panel
+        highlightAttr
+        toplevelFocusRing
+        WorldEditorPanel
+        ( plainBorder
+            -- TODO FIXME
+            & topLabels . rightLabel .~ (drawType <$> (uis ^. uiREPL . replType))
+        )
+        innerWidget
+    else emptyWidget
+ where
+  privateFocusRing = worldEditor ^. editorFocusRing
+  maybeCurrentFocus = focusGetCurrent privateFocusRing
+
+  innerWidget =
+    padLeftRight 1 $
+      hLimit 30 $
+        vBox
+          [ brushWidget
+          , -- , entityWidget
+            areaWidget
+          , outputWidget
+          ]
+
+  worldEditor = uis ^. uiWorldEditor
+  maybeSelectedTerrain = fmap snd $ BL.listSelectedElement $ worldEditor ^. terrainList
+  maybeAreaBounds = worldEditor ^. editingBounds
+
+  -- TODO: Use withFocusRing
+  mkFormControl n w =
+    clickable n $ transformation w
+   where
+    transformation =
+      if Just n == maybeCurrentFocus
+        then withAttr BL.listSelectedFocusedAttr
+        else id
+
+  brushWidget =
+    mkFormControl (WorldEditorPanelControl BrushSelector) $
+      padRight (Pad 1) (str "Brush:") <+> brushWidgetContent
+
+  brushWidgetContent =
+    maybe emptyWidget drawLabeledTerrainSwatch maybeSelectedTerrain
+
+  -- entityWidget =
+  --   mkFormControl (WorldEditorPanelControl EntitySelector) $
+  --     padRight (Pad 1) (str "Entity:") <+> entityWidgetContent
+
+  -- entityWidgetContent =
+  --   maybe emptyWidget drawLabeledTerrainSwatch maybeSelectedTerrain
+
+  areaContent = case worldEditor ^. boundsSelectionStep of
+    UpperLeftPending -> str "Click top-left"
+    LowerRightPending _wcoords -> str "Click bottom-right"
+    SelectionComplete -> maybe emptyWidget renderBounds maybeAreaBounds
+
+  areaWidget =
+    mkFormControl (WorldEditorPanelControl AreaSelector) $
+      vBox
+        [ str "Area:"
+        , areaContent
+        ]
+
+  renderBounds (W.Coords primaryCorner@(x1, y1), W.Coords (x2, y2)) =
+    str $ L.intercalate " @ " [rectSize, show primaryCorner]
+   where
+    width = x2 - x1
+    -- NOTE: The height coordinate is inverted so we do opposite subtraction order here:
+    height = y1 - y2
+    rectSize = L.intercalate "x" [show width, show height]
+
+  outputWidget =
+    mkFormControl (WorldEditorPanelControl OutputPathSelector) $
+      padRight (Pad 1) (str "Output:") <+> outputWidgetContent
+
+  outputWidgetContent = str $ worldEditor ^. outputFilePath
diff --git a/src/Swarm/TUI/Editor/Util.hs b/src/Swarm/TUI/Editor/Util.hs
new file mode 100644
index 0000000000..add6e651de
--- /dev/null
+++ b/src/Swarm/TUI/Editor/Util.hs
@@ -0,0 +1,29 @@
+module Swarm.TUI.Editor.Util where
+
+import Control.Lens hiding (Const, from)
+import Data.Char qualified as DC
+import Data.Int (Int64)
+import Data.Map qualified as Map
+import Data.Maybe qualified as Maybe
+import Swarm.Game.Entity (Entity)
+import Swarm.Game.Terrain (TerrainType)
+import Swarm.Game.World qualified as W
+import Swarm.TUI.Model
+
+getTerrainAt :: WorldEditor -> W.World Int Entity -> W.Coords -> TerrainType
+getTerrainAt editor w coords = case editor ^. isWorldEditorEnabled of
+  True -> Maybe.fromMaybe underlyingCell $ Map.lookup coords paintMap
+  False -> underlyingCell
+ where
+  paintMap = editor ^. paintedTerrain
+  underlyingCell = toEnum $ W.lookupTerrain coords w
+
+getEditedMapAsString :: WorldEditor -> Maybe (W.Coords, W.Coords) -> W.World Int Entity -> String
+getEditedMapAsString _ Nothing _ = "EMPTY BOUNDS"
+getEditedMapAsString worldEditor (Just (W.Coords (xLeft, yTop), W.Coords (xRight, yBottom))) w =
+  unlines $ map renderLine [yTop .. yBottom]
+ where
+  getTerrain = getTerrainAt worldEditor w
+  drawCell :: Int64 -> Int64 -> Char
+  drawCell rowIndex = DC.chr . (+ DC.ord '0') . fromEnum . getTerrain . W.Coords . (rowIndex,)
+  renderLine rowIndex = map (drawCell rowIndex) [xLeft .. xRight]
diff --git a/src/Swarm/TUI/Model.hs b/src/Swarm/TUI/Model.hs
index 63f548b01e..de91e7bbb0 100644
--- a/src/Swarm/TUI/Model.hs
+++ b/src/Swarm/TUI/Model.hs
@@ -60,6 +60,16 @@ module Swarm.TUI.Model (
   _Separator,
   _InventoryEntry,
   _InstalledEntry,
+  WorldEditorFocusable (..),
+  BoundsSelectionStep (..),
+  WorldEditor (..),
+  isWorldEditorEnabled,
+  terrainList,
+  paintedTerrain,
+  editingBounds,
+  boundsSelectionStep,
+  editorFocusRing,
+  outputFilePath,
 
   -- ** UI Model
   UIState,
@@ -68,6 +78,7 @@ module Swarm.TUI.Model (
   uiCheatMode,
   uiFocusRing,
   uiWorldCursor,
+  uiWorldEditor,
   uiREPL,
   uiInventory,
   uiInventorySort,
@@ -199,6 +210,7 @@ import Swarm.Game.ScenarioInfo (
   _SISingle,
  )
 import Swarm.Game.State
+import Swarm.Game.Terrain (TerrainType)
 import Swarm.Game.World qualified as W
 import Swarm.Language.Types
 import Swarm.TUI.Inventory.Sorting
@@ -224,6 +236,13 @@ data AppEvent
   | UpstreamVersion (Either NewReleaseFailure String)
   deriving (Show)
 
+data WorldEditorFocusable
+  = BrushSelector
+  | EntitySelector
+  | AreaSelector
+  | OutputPathSelector
+  deriving (Eq, Ord, Show, Read, Bounded, Enum)
+
 -- | 'Name' represents names to uniquely identify various components
 --   of the UI, such as forms, panels, caches, extents, and lists.
 data Name
@@ -231,6 +250,10 @@ data Name
     REPLPanel
   | -- | The panel containing the world view.
     WorldPanel
+  | -- | The panel containing the world editor controls.
+    WorldEditorPanel
+  | -- | An individual control within the world editor panel.
+    WorldEditorPanelControl WorldEditorFocusable
   | -- | The panel showing robot info and inventory on the top left.
     RobotPanel
   | -- | The info panel on the bottom left.
@@ -241,6 +264,10 @@ data Name
     WorldCache
   | -- | The cached extent for the world view.
     WorldExtent
+  | -- | The list of possible terrain materials.
+    TerrainList
+  | -- | The terrain item position in the TerrainList.
+    TerrainListItem Int
   | -- | The list of inventory items for the currently
     --   focused robot.
     InventoryList
@@ -483,6 +510,7 @@ data ModalType
   | KeepPlayingModal
   | DescriptionModal Entity
   | GoalModal [Text]
+  | TerrainPaletteModal
   deriving (Eq, Show)
 
 data ButtonSelection = CancelButton | KeepPlayingButton | StartOverButton Seed ScenarioInfoPair | QuitButton | NextButton ScenarioInfoPair
@@ -557,6 +585,37 @@ makePrisms ''InventoryListEntry
 -- UI state
 ------------------------------------------------------------
 
+data BoundsSelectionStep
+  = UpperLeftPending
+  | -- | Stores the *mouse coords* of the upper-left click
+    LowerRightPending W.Coords
+  | SelectionComplete
+
+data WorldEditor = WorldEditor
+  { _isWorldEditorEnabled :: Bool
+  , _terrainList :: BL.List Name TerrainType
+  , _paintedTerrain :: M.Map W.Coords TerrainType
+  , -- | Upper-left and lower-right coordinates
+    -- of the map to be saved.
+    _editingBounds :: Maybe (W.Coords, W.Coords)
+  , _boundsSelectionStep :: BoundsSelectionStep
+  , _editorFocusRing :: FocusRing Name
+  , _outputFilePath :: FilePath
+  }
+
+makeLenses ''WorldEditor
+
+initialWorldEditor :: WorldEditor
+initialWorldEditor =
+  WorldEditor
+    False
+    (BL.list TerrainList (V.fromList listEnums) 1)
+    mempty
+    (Just (W.Coords (-10, -10), W.Coords (10, 10)))
+    SelectionComplete
+    (focusRing $ map WorldEditorPanelControl listEnums)
+    "output.txt"
+
 -- | The main record holding the UI state.  For access to the fields,
 -- see the lenses below.
 data UIState = UIState
@@ -565,6 +624,7 @@ data UIState = UIState
   , _uiCheatMode :: Bool
   , _uiFocusRing :: FocusRing Name
   , _uiWorldCursor :: Maybe W.Coords
+  , _uiWorldEditor :: WorldEditor
   , _uiREPL :: REPLState
   , _uiInventory :: Maybe (Int, BL.List Name InventoryListEntry)
   , _uiInventorySort :: InventorySortOptions
@@ -621,6 +681,9 @@ uiFocusRing :: Lens' UIState (FocusRing Name)
 -- | The last clicked position on the world view.
 uiWorldCursor :: Lens' UIState (Maybe W.Coords)
 
+-- | World editor mode
+uiWorldEditor :: Lens' UIState WorldEditor
+
 -- | The state of REPL panel.
 uiREPL :: Lens' UIState REPLState
 
@@ -819,8 +882,18 @@ focusedEntity =
 -- UIState initialization
 
 -- | The initial state of the focus ring.
+-- NOTE: Normally, the Tab key might cycle through the members of the
+-- focus ring. However, the REPL already uses Tab. So, to is not used
+-- at all right now for navigating the toplevel focus ring.
 initFocusRing :: FocusRing Name
-initFocusRing = focusRing [REPLPanel, InfoPanel, RobotPanel, WorldPanel]
+initFocusRing =
+  focusRing
+    [ REPLPanel
+    , InfoPanel
+    , RobotPanel
+    , WorldPanel
+    , WorldEditorPanel
+    ]
 
 -- | The initial tick speed.
 initLgTicksPerSecond :: Int
@@ -844,6 +917,7 @@ initUIState showMainMenu cheatMode = liftIO $ do
       , _uiCheatMode = cheatMode
       , _uiFocusRing = initFocusRing
       , _uiWorldCursor = Nothing
+      , _uiWorldEditor = initialWorldEditor
       , _uiREPL = initREPLState $ newREPLHistory history
       , _uiInventory = Nothing
       , _uiInventorySort = defaultSortOptions
diff --git a/src/Swarm/TUI/View.hs b/src/Swarm/TUI/View.hs
index 690226c300..3138be6a16 100644
--- a/src/Swarm/TUI/View.hs
+++ b/src/Swarm/TUI/View.hs
@@ -14,7 +14,6 @@ module Swarm.TUI.View (
 
   -- * Dialog box
   drawDialog,
-  generateModal,
   chooseCursor,
 
   -- * Key hint menu
@@ -86,17 +85,19 @@ import Swarm.Game.ScenarioInfo (
   scenarioStatus,
  )
 import Swarm.Game.State
-import Swarm.Game.Terrain (terrainMap)
+import Swarm.Game.Terrain (TerrainType, terrainMap)
 import Swarm.Game.World qualified as W
 import Swarm.Language.Pretty (prettyText)
 import Swarm.Language.Syntax
 import Swarm.Language.Typecheck (inferConst)
-import Swarm.Language.Types (Polytype)
 import Swarm.TUI.Attr
 import Swarm.TUI.Border
+import Swarm.TUI.Editor.EditorView qualified as EV
+import Swarm.TUI.Editor.Util qualified as EU
 import Swarm.TUI.Inventory.Sorting (renderSortMethod)
 import Swarm.TUI.Model
 import Swarm.TUI.Panel
+import Swarm.TUI.View.ViewUtils
 import Swarm.Util
 import Swarm.Version (NewReleaseFailure (..))
 import System.Clock (TimeSpec (..))
@@ -295,21 +296,29 @@ drawGameUI s =
                     & addCursorPos
                     & addClock
                 )
-                (drawWorld (s ^. uiState . uiShowRobots) (s ^. gameState))
+                ( drawWorld
+                    (s ^. uiState . uiShowRobots)
+                    (s ^. uiState . uiWorldEditor)
+                    (s ^. gameState)
+                )
             , drawKeyMenu s
-            , clickable REPLPanel $
-                panel
-                  highlightAttr
-                  fr
-                  REPLPanel
-                  ( plainBorder
-                      & topLabels . rightLabel .~ (drawType <$> (s ^. uiState . uiREPL . replType))
-                  )
-                  ( vLimit replHeight
-                      . padBottom Max
-                      . padLeftRight 1
-                      $ drawREPL s
-                  )
+            , hBox
+                [ clickable REPLPanel $
+                    panel
+                      highlightAttr
+                      fr
+                      REPLPanel
+                      ( plainBorder
+                          & topLabels . rightLabel .~ (drawType <$> (s ^. uiState . uiREPL . replType))
+                      )
+                      ( vLimit replHeight
+                          . padBottom Max
+                          . padLeftRight 1
+                          $ drawREPL s
+                      )
+                , clickable WorldEditorPanel $
+                    EV.drawWorldEditor fr $ s ^. uiState
+                ]
             ]
         ]
   ]
@@ -317,7 +326,7 @@ drawGameUI s =
   addCursorPos = case s ^. uiState . uiWorldCursor of
     Nothing -> id
     Just coord ->
-      let worldCursorInfo = drawWorldCursorInfo (s ^. gameState) coord
+      let worldCursorInfo = drawWorldCursorInfo (s ^. uiState . uiWorldEditor) (s ^. gameState) coord
        in bottomLabels . leftLabel ?~ padLeftRight 1 worldCursorInfo
   -- Add clock display in top right of the world view if focused robot
   -- has a clock installed
@@ -326,8 +335,8 @@ drawGameUI s =
   moreTop = s ^. uiState . uiMoreInfoTop
   moreBot = s ^. uiState . uiMoreInfoBot
 
-drawWorldCursorInfo :: GameState -> W.Coords -> Widget Name
-drawWorldCursorInfo g coords@(W.Coords (y, x)) =
+drawWorldCursorInfo :: WorldEditor -> GameState -> W.Coords -> Widget Name
+drawWorldCursorInfo worldEditor g coords@(W.Coords (y, x)) =
   hBox $ tileMemberWidgets ++ [coordsWidget]
  where
   coordsWidget =
@@ -346,7 +355,7 @@ drawWorldCursorInfo g coords@(W.Coords (y, x)) =
    where
     f cell preposition = [renderDisplay cell, txt preposition]
 
-  terrain = displayTerrainCell g coords
+  terrain = displayTerrainCell worldEditor g coords
   entity = displayEntityCell g coords
   robot = displayRobotCell g coords
 
@@ -389,10 +398,6 @@ drawTime t showTicks =
 maybeDrawTime :: Integer -> Bool -> GameState -> Maybe (Widget n)
 maybeDrawTime t showTicks gs = guard (clockInstalled gs) $> drawTime t showTicks
 
--- | Render the type of the current REPL input to be shown to the user.
-drawType :: Polytype -> Widget Name
-drawType = withAttr infoAttr . padLeftRight 1 . txt . prettyText
-
 -- | Draw info about the current number of ticks per second.
 drawTPS :: AppState -> Widget Name
 drawTPS s = hBox (tpsInfo : rateInfo)
@@ -425,10 +430,6 @@ chooseCursor s locs = case s ^. uiState . uiModal of
   Nothing -> showFirstCursor s locs
   Just _ -> Nothing
 
--- | Width cap for modal and error message windows
-maxModalWindowWidth :: Int
-maxModalWindowWidth = 500
-
 -- | Render the error dialog window with a given error message
 renderErrorDialog :: Text -> Widget Name
 renderErrorDialog err = renderDialog (dialog (Just "Error") Nothing (maxModalWindowWidth `min` requiredWidth)) errContent
@@ -471,77 +472,19 @@ drawModal s = \case
   QuitModal -> padBottom (Pad 1) $ hCenter $ txt (quitMsg (s ^. uiState . uiMenu))
   GoalModal g -> padLeftRight 1 (displayParagraphs g)
   KeepPlayingModal -> padLeftRight 1 (displayParagraphs ["Have fun!  Hit Ctrl-Q whenever you're ready to proceed to the next challenge or return to the menu."])
+  TerrainPaletteModal -> drawTerrainSelector s
 
-quitMsg :: Menu -> Text
-quitMsg m = "Are you sure you want to " <> quitAction <> "? All progress on this scenario will be lost!"
- where
-  quitAction = case m of
-    NoMenu -> "quit"
-    _ -> "return to the menu"
+drawTerrainSelector :: AppState -> Widget Name
+drawTerrainSelector s =
+  padAll 1 $
+    hCenter $
+      vLimit (length (listEnums :: [TerrainType])) $
+        BL.renderListWithIndex listDrawTerrainElement True $
+          s ^. uiState . uiWorldEditor . terrainList
 
--- | Generate a fresh modal window of the requested type.
-generateModal :: AppState -> ModalType -> Modal
-generateModal s mt = Modal mt (dialog (Just title) buttons (maxModalWindowWidth `min` requiredWidth))
- where
-  currentScenario = s ^. uiState . scenarioRef
-  currentSeed = s ^. gameState . seed
-  haltingMessage = case s ^. uiState . uiMenu of
-    NoMenu -> Just "Quit"
-    _ -> Nothing
-  descriptionWidth = 100
-  helpWidth = 80
-  (title, buttons, requiredWidth) =
-    case mt of
-      HelpModal -> (" Help ", Nothing, helpWidth)
-      RobotsModal -> ("Robots", Nothing, descriptionWidth)
-      RecipesModal -> ("Available Recipes", Nothing, descriptionWidth)
-      CommandsModal -> ("Available Commands", Nothing, descriptionWidth)
-      MessagesModal -> ("Messages", Nothing, descriptionWidth)
-      WinModal ->
-        let nextMsg = "Next challenge!"
-            stopMsg = fromMaybe "Return to the menu" haltingMessage
-            continueMsg = "Keep playing"
-         in ( ""
-            , Just
-                ( 0
-                , [ (nextMsg, NextButton scene)
-                  | Just scene <- [nextScenario (s ^. uiState . uiMenu)]
-                  ]
-                    ++ [ (stopMsg, QuitButton)
-                       , (continueMsg, KeepPlayingButton)
-                       ]
-                )
-            , sum (map length [nextMsg, stopMsg, continueMsg]) + 32
-            )
-      DescriptionModal e -> (descriptionTitle e, Nothing, descriptionWidth)
-      QuitModal ->
-        let stopMsg = fromMaybe ("Quit to" ++ maybe "" (" " ++) (into @String <$> curMenuName s) ++ " menu") haltingMessage
-            maybeStartOver = sequenceA ("Start over", StartOverButton currentSeed <$> currentScenario)
-         in ( ""
-            , Just
-                ( 0
-                , catMaybes
-                    [ Just ("Keep playing", CancelButton)
-                    , maybeStartOver
-                    , Just (stopMsg, QuitButton)
-                    ]
-                )
-            , T.length (quitMsg (s ^. uiState . uiMenu)) + 4
-            )
-      GoalModal _ ->
-        let goalModalTitle = case currentScenario of
-              Nothing -> "Goal"
-              Just (scenario, _) -> scenario ^. scenarioName
-         in (" " <> T.unpack goalModalTitle <> " ", Nothing, 80)
-      KeepPlayingModal -> ("", Just (0, [("OK", CancelButton)]), 80)
-
--- | Get the name of the current New Game menu.
-curMenuName :: AppState -> Maybe Text
-curMenuName s = case s ^. uiState . uiMenu of
-  NewGameMenu (_ :| (parentMenu : _)) ->
-    Just (parentMenu ^. BL.listSelectedElementL . to scenarioItemName)
-  NewGameMenu _ -> Just "Scenarios"
-  _ -> Nothing
+listDrawTerrainElement :: Int -> Bool -> TerrainType -> Widget Name
+listDrawTerrainElement pos _isSelected a =
+  clickable (TerrainListItem pos) $ drawLabeledTerrainSwatch a
 
 robotsListWidget :: AppState -> Widget Name
 robotsListWidget s = hCenter table
@@ -594,7 +537,12 @@ robotsListWidget s = hCenter table
     locWidget = hBox [worldCell, txt $ " " <> locStr]
      where
       rloc@(V2 x y) = robot ^. robotLocation
-      worldCell = drawLoc (s ^. uiState . uiShowRobots) g (W.locToCoords rloc)
+      worldCell =
+        drawLoc
+          (s ^. uiState . uiShowRobots)
+          (s ^. uiState . uiWorldEditor)
+          g
+          (W.locToCoords rloc)
       locStr = from (show x) <> " " <> from (show y)
 
     statusWidget = case robot ^. machine of
@@ -712,9 +660,6 @@ drawConst c = hBox [padLeft (Pad $ 13 - T.length constName) (txt constName), txt
   constName = syntax . constInfo $ c
   constSig = " : " <> prettyText (inferConst c)
 
-descriptionTitle :: Entity -> String
-descriptionTitle e = " " ++ from @Text (e ^. entityName) ++ " "
-
 -- | Generate a pop-up widget to display the description of an entity.
 descriptionWidget :: AppState -> Entity -> Widget Name
 descriptionWidget s e = padLeftRight 1 (explainEntry s e)
@@ -817,6 +762,7 @@ drawKeyMenu s =
     catMaybes
       [ may goal (NoHighlight, "^g", "goal")
       , may cheat (NoHighlight, "^v", "creative")
+      , may cheat (NoHighlight, "^e", "editor")
       , Just (NoHighlight, "^p", if isPaused then "unpause" else "pause")
       , Just (NoHighlight, "^o", "step")
       , Just (NoHighlight, "^zx", "speed")
@@ -828,6 +774,8 @@ drawKeyMenu s =
     "pop out" | (s ^. uiState . uiMoreInfoBot) || (s ^. uiState . uiMoreInfoTop) -> Alert
     _ -> PanelSpecific
 
+  keyCmdsFor (Just WorldEditorPanel) =
+    [("^s", "save map")]
   keyCmdsFor (Just REPLPanel) =
     [ ("↓↑", "history")
     ]
@@ -868,8 +816,8 @@ drawKeyCmd (h, key, cmd) =
 ------------------------------------------------------------
 
 -- | Draw the current world view.
-drawWorld :: Bool -> GameState -> Widget Name
-drawWorld showRobots g =
+drawWorld :: Bool -> WorldEditor -> GameState -> Widget Name
+drawWorld showRobots we g =
   center
     . cached WorldCache
     . reportExtent WorldExtent
@@ -881,14 +829,15 @@ drawWorld showRobots g =
       let w = ctx ^. availWidthL
           h = ctx ^. availHeightL
           ixs = range (viewingRegion g (fromIntegral w, fromIntegral h))
-      render . vBox . map hBox . chunksOf w . map (drawLoc showRobots g) $ ixs
+      render . vBox . map hBox . chunksOf w . map (drawLoc showRobots we g) $ ixs
 
 -- | Render the 'Display' for a specific location.
-drawLoc :: Bool -> GameState -> W.Coords -> Widget Name
-drawLoc showRobots g = renderDisplay . displayLoc showRobots g
+drawLoc :: Bool -> WorldEditor -> GameState -> W.Coords -> Widget Name
+drawLoc showRobots we g = renderDisplay . displayLoc showRobots we g
 
-displayTerrainCell :: GameState -> W.Coords -> Display
-displayTerrainCell g coords = terrainMap M.! toEnum (W.lookupTerrain coords (g ^. world))
+displayTerrainCell :: WorldEditor -> GameState -> W.Coords -> Display
+displayTerrainCell worldEditor g coords =
+  terrainMap M.! EU.getTerrainAt worldEditor (g ^. world) coords
 
 displayEntityCell, displayRobotCell :: GameState -> W.Coords -> [Display]
 displayRobotCell g coords = map (view robotDisplay) (robotsAtLocation (W.coordsToLoc coords) g)
@@ -907,11 +856,11 @@ displayEntityCell g coords = maybeToList (displayForEntity <$> W.lookupEntity co
 
 -- | Get the 'Display' for a specific location, by combining the
 --   'Display's for the terrain, entity, and robots at the location.
-displayLoc :: Bool -> GameState -> W.Coords -> Display
-displayLoc showRobots g coords =
+displayLoc :: Bool -> WorldEditor -> GameState -> W.Coords -> Display
+displayLoc showRobots worldEditor g coords =
   sconcat $ terrain NE.:| entity <> robots
  where
-  terrain = displayTerrainCell g coords
+  terrain = displayTerrainCell worldEditor g coords
   entity = displayEntityCell g coords
   robots =
     if showRobots
diff --git a/src/Swarm/TUI/View/ViewUtils.hs b/src/Swarm/TUI/View/ViewUtils.hs
new file mode 100644
index 0000000000..6bba60a6e4
--- /dev/null
+++ b/src/Swarm/TUI/View/ViewUtils.hs
@@ -0,0 +1,118 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module Swarm.TUI.View.ViewUtils where
+
+import Brick hiding (Direction)
+import Brick.Widgets.Dialog
+import Brick.Widgets.List qualified as BL
+import Control.Lens hiding (Const, from)
+import Data.List.NonEmpty (NonEmpty (..))
+import Data.Map qualified as M
+import Data.Maybe (catMaybes, fromMaybe)
+import Data.Text (Text)
+import Data.Text qualified as T
+import Swarm.Game.Display
+import Swarm.Game.Entity as E
+import Swarm.Game.Scenario (scenarioName)
+import Swarm.Game.ScenarioInfo (scenarioItemName)
+import Swarm.Game.State
+import Swarm.Game.Terrain (TerrainType, terrainMap)
+import Swarm.Language.Pretty (prettyText)
+import Swarm.Language.Types (Polytype)
+import Swarm.TUI.Attr
+import Swarm.TUI.Model
+import Swarm.Util
+import Witch (from, into)
+
+-- | Generate a fresh modal window of the requested type.
+generateModal :: AppState -> ModalType -> Modal
+generateModal s mt = Modal mt (dialog (Just title) buttons (maxModalWindowWidth `min` requiredWidth))
+ where
+  currentScenario = s ^. uiState . scenarioRef
+  currentSeed = s ^. gameState . seed
+  haltingMessage = case s ^. uiState . uiMenu of
+    NoMenu -> Just "Quit"
+    _ -> Nothing
+  descriptionWidth = 100
+  helpWidth = 80
+  (title, buttons, requiredWidth) =
+    case mt of
+      HelpModal -> (" Help ", Nothing, helpWidth)
+      RobotsModal -> ("Robots", Nothing, descriptionWidth)
+      RecipesModal -> ("Available Recipes", Nothing, descriptionWidth)
+      CommandsModal -> ("Available Commands", Nothing, descriptionWidth)
+      MessagesModal -> ("Messages", Nothing, descriptionWidth)
+      WinModal ->
+        let nextMsg = "Next challenge!"
+            stopMsg = fromMaybe "Return to the menu" haltingMessage
+            continueMsg = "Keep playing"
+         in ( ""
+            , Just
+                ( 0
+                , [ (nextMsg, NextButton scene)
+                  | Just scene <- [nextScenario (s ^. uiState . uiMenu)]
+                  ]
+                    ++ [ (stopMsg, QuitButton)
+                       , (continueMsg, KeepPlayingButton)
+                       ]
+                )
+            , sum (map length [nextMsg, stopMsg, continueMsg]) + 32
+            )
+      DescriptionModal e -> (descriptionTitle e, Nothing, descriptionWidth)
+      QuitModal ->
+        let stopMsg = fromMaybe ("Quit to" ++ maybe "" (" " ++) (into @String <$> curMenuName s) ++ " menu") haltingMessage
+            maybeStartOver = sequenceA ("Start over", StartOverButton currentSeed <$> currentScenario)
+         in ( ""
+            , Just
+                ( 0
+                , catMaybes
+                    [ Just ("Keep playing", CancelButton)
+                    , maybeStartOver
+                    , Just (stopMsg, QuitButton)
+                    ]
+                )
+            , T.length (quitMsg (s ^. uiState . uiMenu)) + 4
+            )
+      GoalModal _ ->
+        let goalModalTitle = case currentScenario of
+              Nothing -> "Goal"
+              Just (scenario, _) -> scenario ^. scenarioName
+         in (" " <> T.unpack goalModalTitle <> " ", Nothing, 80)
+      KeepPlayingModal -> ("", Just (0, [("OK", CancelButton)]), 80)
+      TerrainPaletteModal -> ("Terrain", Nothing, w)
+       where
+        wordLength = maximum $ map (length . show) (listEnums :: [TerrainType])
+        w = wordLength + 6
+
+-- | Render the type of the current REPL input to be shown to the user.
+drawType :: Polytype -> Widget Name
+drawType = withAttr infoAttr . padLeftRight 1 . txt . prettyText
+
+drawLabeledTerrainSwatch :: TerrainType -> Widget Name
+drawLabeledTerrainSwatch a =
+  tile <+> str materialName
+ where
+  tile = padRight (Pad 1) $ renderDisplay $ terrainMap M.! a
+  materialName = init $ show a
+
+descriptionTitle :: Entity -> String
+descriptionTitle e = " " ++ from @Text (e ^. entityName) ++ " "
+
+-- | Width cap for modal and error message windows
+maxModalWindowWidth :: Int
+maxModalWindowWidth = 500
+
+-- | Get the name of the current New Game menu.
+curMenuName :: AppState -> Maybe Text
+curMenuName s = case s ^. uiState . uiMenu of
+  NewGameMenu (_ :| (parentMenu : _)) ->
+    Just (parentMenu ^. BL.listSelectedElementL . to scenarioItemName)
+  NewGameMenu _ -> Just "Scenarios"
+  _ -> Nothing
+
+quitMsg :: Menu -> Text
+quitMsg m = "Are you sure you want to " <> quitAction <> "? All progress on this scenario will be lost!"
+ where
+  quitAction = case m of
+    NoMenu -> "quit"
+    _ -> "return to the menu"
diff --git a/swarm.cabal b/swarm.cabal
index 9a5695a52b..e05d467e8b 100644
--- a/swarm.cabal
+++ b/swarm.cabal
@@ -111,10 +111,15 @@ library
                       Swarm.Game.WorldGen
                       Swarm.TUI.Attr
                       Swarm.TUI.Border
+                      Swarm.TUI.Controller.ControllerUtils
+                      Swarm.TUI.Editor.EditorController
+                      Swarm.TUI.Editor.Util
+                      Swarm.TUI.Editor.EditorView
                       Swarm.TUI.List
                       Swarm.TUI.Panel
                       Swarm.TUI.Model
                       Swarm.TUI.View
+                      Swarm.TUI.View.ViewUtils
                       Swarm.TUI.Controller
                       Swarm.TUI.Inventory.Sorting
                       Swarm.App