diff --git a/builtins.ts b/builtins.ts
index e43706a..ec79209 100644
--- a/builtins.ts
+++ b/builtins.ts
@@ -5,10 +5,10 @@ import {
 } from "./window.ts";
 import { font } from "./font.ts";
 // import { keyDown, keyPressed, keyReleased } from "./keyboard.ts";
-import { addToContext } from "./runcode.ts";
+import { addToContext, runCode } from "./runcode.ts";
 import { resetRepl } from "./repl.ts";
 import { COLOR } from "./colors.ts";
-import { getSheet } from "./sheet.ts";
+import { getSheet, getCodeSheet } from "./sheet.ts";
 
 export const drawSprite = (x: number, y: number, spr: number) => {
 	const {sheet_type, value: sprites} = getSheet(2);
@@ -43,6 +43,9 @@ const faux = {
 	// key_down: keyDown,
 	// key_pressed: keyPressed,
 	// key_released: keyReleased,
+	code: (n: number) => {
+		return runCode(getCodeSheet(n));
+	},
 	log: console.log,
 	JSON: JSON,
 };
diff --git a/codetab.ts b/codetab.ts
index bec6745..44520cf 100644
--- a/codetab.ts
+++ b/codetab.ts
@@ -2,11 +2,49 @@ import { clearScreen, fillRect } from "./window.ts";
 import { fontWidth, fontHeight } from "./font.ts";
 import { drawText } from "./builtins.ts";
 import { COLOR } from "./colors.ts";
-import {getSheet, setSheet} from "./sheet.ts";
+import {getCodeSheet, setSheet} from "./sheet.ts";
 import { K, ctrlKeyDown, getKeyboardString, keyPressed, shiftKeyDown } from "./keyboard.ts";
 import { clipboard, tokenize } from "./deps.ts";
 
+const historyDebounceFrames = 20;
+
 const state = {
+	history: [{code: getCodeSheet(0), anchor: 0, focus: 0}],
+	historyDebounce: 0,
+	historyIndex: 0,
+	undo() {
+		if (this.historyIndex === this.history.length && this.historyDebounce > 0) {
+			this.snapshot();
+		}
+		if (this.historyIndex > 0) {
+			this.historyIndex -= 1;
+			const snap = this.history[this.historyIndex];
+			this.code = snap.code;
+			this.setSelection(snap.anchor, snap.focus);
+		}
+	},
+	redo() {
+		if (this.historyIndex < this.history.length-1) {
+			this.historyIndex += 1;
+			const snap = this.history[this.historyIndex];
+			this.code = snap.code;
+			this.setSelection(snap.anchor, snap.focus);
+		}
+	},
+	snapshot() {
+		this.history.push({
+			code: this.code,
+			anchor: this.anchor,
+			focus: this.focus,
+		});
+	},
+	startSnapping() {
+		this.historyIndex += 1;
+		if (this.history.length > this.historyIndex) {
+			this.history.length = this.historyIndex;
+		}
+		this.historyDebounce = historyDebounceFrames;
+	},
 	scrollX: 0,
 	scrollY: 0,
 	anchor: 0,
@@ -42,6 +80,7 @@ const state = {
 		const {code, anchor, focus} = this;
 		this.code = code.slice(0, Math.min(anchor, focus)) + text + code.slice(Math.max(anchor, focus));
 		this.setSelection(Math.min(anchor, focus) + text.length);
+		this.startSnapping();
 	},
 	indent(indentString: string) {
 		const lines = this.code.split("\n");
@@ -55,6 +94,7 @@ const state = {
 		});
 		this.code = newLines.join("\n");
 		this.setSelection({x: anchorX+1, y: anchorY}, {x: focusX+1, y: focusY});
+		this.startSnapping();
 	},
 	outdent(outdentRegex: RegExp) {
 		const lines = this.code.split("\n");
@@ -69,6 +109,7 @@ const state = {
 		});
 		this.code = newLines.join("\n");
 		this.setSelection({x: Math.max(0,anchorX-1), y: anchorY}, {x: Math.max(0,focusX-1), y: focusY});
+		this.startSnapping();
 	},
 	backspace() {
 		const {code, focus} = this;
@@ -76,6 +117,7 @@ const state = {
 			if (focus > 0) {
 				this.code = code.slice(0, focus-1) + code.slice(focus);
 				this.setSelection(focus-1);
+				this.startSnapping();
 			}
 		} else {
 			this.insertText("");
@@ -86,6 +128,7 @@ const state = {
 		if (this.isCollapsed()) {
 			if (focus < code.length) {
 				this.code = code.slice(0, focus) + code.slice(1+focus);
+				this.startSnapping();
 			}
 		} else {
 			this.insertText("");
@@ -101,7 +144,6 @@ const state = {
 		this.insertText("");
 	},
 	async paste() {
-
 		this.insertText(await clipboard.readText());
 	},
 	scrollToCursor() {
@@ -122,11 +164,7 @@ const state = {
 		}
 	},
 	get code() {
-		const {sheet_type, value} = getSheet(0);
-		if (sheet_type !== "code") {
-			throw "Trying to run a non-code sheet as code."
-		}
-		return value;
+		return getCodeSheet(0);
 	},
 	set code(val) {
 		setSheet(0, "code", val);
@@ -347,12 +385,18 @@ const drawCodeField = (code: string, x: number, y: number, w: number, h: number)
 
 const update = async () => {
 	const { focus, focusX, focusY} = state;
+	if (state.historyDebounce > 0) {
+		state.historyDebounce -= 1;
+		if (state.historyDebounce <= 0) {
+			state.snapshot();
+		}
+	}
+
 	const keyboardString = getKeyboardString();
 	if (keyboardString) {
 		state.insertText(keyboardString);
 		state.scrollToCursor();
 	}
-	// TODO: Handle ctrl-Z
 	// TODO: Make ctrl-/ do commenting out (take inspiration from tab)
 
 	if (keyPressed(K.ENTER)) {
@@ -414,12 +458,25 @@ const update = async () => {
 	}
 	if (keyPressed("C") && ctrlKeyDown()) {
 		await state.copy();
+		state.scrollToCursor();
 	}
 	if (keyPressed("X") && ctrlKeyDown()) {
 		await state.cut();
+		state.scrollToCursor();
 	}
 	if (keyPressed("V") && ctrlKeyDown()) {
 		await state.paste();
+		state.scrollToCursor();
+	}
+	if (keyPressed("Z") && ctrlKeyDown()) {
+		if (shiftKeyDown()) {
+			state.redo();
+		} else {
+			state.undo();
+		}
+	}
+	if (keyPressed("Y") && ctrlKeyDown()) {
+		state.redo();
 	}
 }
 
diff --git a/index.ts b/index.ts
index acb29f8..11ec162 100644
--- a/index.ts
+++ b/index.ts
@@ -3,7 +3,8 @@ import {
 	frame,
 	clearScreen,
 } from "./window.ts";
-import { codeSheet } from "./sheet.ts";
+import { runCode } from "./runcode.ts";
+import { getCodeSheet } from "./sheet.ts";
 import { refreshKeyboard, keyPressed, K } from "./keyboard.ts";
 import { repl, resetRepl } from "./repl.ts";
 import { addToContext } from "./runcode.ts";
@@ -17,7 +18,7 @@ let mode: "play" | "edit" | "repl" = "repl";
 
 addToContext("play", () => {
 	mode = "play";
-	game = codeSheet(0);
+	game = runCode(getCodeSheet(0));
 	game.init();
 });
 
diff --git a/sheet.ts b/sheet.ts
index 3995fd2..08704dc 100644
--- a/sheet.ts
+++ b/sheet.ts
@@ -1,5 +1,5 @@
 import { getCart } from "./cart.ts";
-import { runCode, addToContext } from "./runcode.ts";
+// import { runCode, addToContext } from "./runcode.ts";
 
 // "code" | "spritesheet" | "map" | "sfx" | "patterns" | "fonts"
 export type Sheet = {
@@ -20,12 +20,20 @@ export const setSheet = (n: number, type: SheetType, value: any) => {
 	return getCart()[n] = {sheet_type: type, value};
 }
 
-export const codeSheet = (sheet: number) => {
+export const getCodeSheet = (sheet: number) => {
 	const {sheet_type, value} = getSheet(sheet);
 	if (sheet_type !== "code") {
-		throw "Trying to run a non-code sheet as code."
+		throw "Trying to use a non-code sheet as code."
 	}
-	return runCode(value);
+	return value;
 }
 
-addToContext("code_sheet", codeSheet);
\ No newline at end of file
+export const getSpriteSheet = (sheet: number) => {
+	const {sheet_type, value} = getSheet(sheet);
+	if (sheet_type !== "spritesheet") {
+		throw "Trying to use a non-sprite sheet as a spritesheet."
+	}
+	return value;
+}
+
+// addToContext("code", codeSheet);
\ No newline at end of file