diff --git a/takhta.html b/takhta.html
index d08b720..2e494ec 100644
--- a/takhta.html
+++ b/takhta.html
@@ -306,6 +306,10 @@
 					case 'h':
 						piece = 'P';
 						break;
+					case 'O':
+					case '0':
+						// Castling, handled in its own function
+						return doCastle(move);
 					default:
 						return {error: 'Not a valid piece: ' + piece};
 				}
@@ -435,6 +439,125 @@
 				return {}
 			}
 
+			function doCastle(move) {
+				let ballChar = move[0];
+
+				// Figure out distance between king and rook
+				let emptySquares = 1;
+				let index = 1;
+				while (index < move.length) {
+					if (move.slice(index, index + 2) === '-' + ballChar) {
+						emptySquares += 1;
+						index += 2;
+					} else {
+						break;
+					}
+				}
+
+				// Check(mate)
+				if (!['', '+', '++', '#'].includes(move.slice(index))) {
+					// TODO: Implement handling
+					return {error: 'Unexpected contents at the end of the move: ' + move.slice(index)};
+				}
+
+				// Find the king(s)
+				let whiteMove = document.getElementById('tomove').childNodes[0].data === 'White';
+				let renderedKing = whiteMove ? '♔' : '♚';
+				let renderedRook = whiteMove ? '♖' : '♜';
+
+				let kings = [];
+				for (let kingLetter of 'abcdefgh') {
+					for (let kingNumber of '12345678') {
+						let square = document.getElementById(kingLetter + kingNumber);
+						if (square.childNodes.length !== 0 && square.childNodes[0].data === renderedKing) {
+							kings.push([kingLetter, kingNumber]);
+						}
+					}
+				}
+
+				// Find the rook(s)
+				function squareDiff(squareLetter, squareNumber, dLetter, dNumber) {
+					let x = 'abcdefgh'.indexOf(squareLetter) + dLetter;
+					let y = '12345678'.indexOf(squareNumber) + dNumber;
+					if (x < 0 || x > 7 || y < 0 || y > 7) {
+						// Would be outside of the board
+						return null;
+					}
+					return ['abcdefgh'[x], '12345678'[y]]
+				}
+
+				let distance = emptySquares + 1;
+				let possiblePairs = [];
+				for (let [kingLetter, kingNumber] of kings) {
+					for (let [dLetter, dNumber] of [[-distance, 0], [distance, 0], [0, -distance], [0, distance]]) {
+						let rookCoords = squareDiff(kingLetter, kingNumber, dLetter, dNumber);
+						if (rookCoords === null) {
+							continue;
+						}
+						let [rookLetter, rookNumber] = rookCoords;
+
+						let square = document.getElementById(rookLetter + rookNumber);
+						if (square.childNodes.length !== 0 && square.childNodes[0].data === renderedRook) {
+							possiblePairs.push([kingLetter, kingNumber, rookLetter, rookNumber, dLetter, dNumber]);
+						}
+					}
+				}
+
+				if (possiblePairs.length === 0) {
+					return {error: 'Could not find king and rook matching castling criteria'};
+				} else if (possiblePairs.length > 1) {
+					return {error: 'Found ' + String(possiblePairs.length) + ' possible pairs of king and rook to castle'};
+				}
+
+				let [kingLetter, kingNumber, rookLetter, rookNumber, dLetter, dNumber] = possiblePairs[0];
+				let kingStartSquare = document.getElementById(kingLetter + kingNumber);
+				let rookStartSquare = document.getElementById(rookLetter + rookNumber);
+
+				// Make sure there there are no pieces between the king and the rook
+				let signLetter = Math.sign(dLetter);
+				let signNumber = Math.sign(dNumber);
+				let [squareLetter, squareNumber] = squareDiff(kingLetter, kingNumber, signLetter, signNumber);
+				while (squareLetter !== rookLetter || squareNumber !== rookNumber) {
+					if (document.getElementById(squareLetter + squareNumber).childNodes.length !== 0) {
+						return {error: squareLetter + squareNumber + ' is occupied'};
+					}
+					[squareLetter, squareNumber] = squareDiff(squareLetter, squareNumber, signLetter, signNumber);
+				}
+
+				// King moves two squares towards rook
+				let [kingEndLetter, kingEndNumber] = squareDiff(kingLetter, kingNumber, 2 * signLetter, 2 * signNumber);
+				let kingEndSquare = document.getElementById(kingEndLetter + kingEndNumber);
+
+				// Rook moves to the square king crossed
+				let [rookEndLetter, rookEndNumber] = squareDiff(kingLetter, kingNumber, signLetter, signNumber);
+				let rookEndSquare = document.getElementById(rookEndLetter + rookEndNumber);
+
+				// Move pieces
+				kingStartSquare.removeChild(kingStartSquare.childNodes[0]);
+				rookStartSquare.removeChild(rookStartSquare.childNodes[0]);
+				kingEndSquare.appendChild(document.createTextNode(renderedKing));
+				rookEndSquare.appendChild(document.createTextNode(renderedRook));
+
+				// Flip whose turn it is
+				document.getElementById('tomove').childNodes[0].data = whiteMove ? 'Black' : 'White';
+
+				// Record our alterations to the table
+				let removedPieces = {};
+				let placedPieces = {};
+				removedPieces[kingLetter + kingNumber] = renderedKing;
+				removedPieces[rookLetter + rookNumber] = renderedRook;
+				placedPieces[kingEndLetter + kingEndNumber] = renderedKing;
+				placedPieces[rookEndLetter + rookEndNumber] = renderedRook;
+				let moveRecord = {
+					removedPieces: removedPieces,
+					placedPieces: placedPieces,
+					moveText: move
+				};
+				moveHistory.push(moveRecord);
+
+				return {}
+			}
+
 			function undoMove() {
 				if (moveHistory.length === 0) {
 					alert('No moves to undo');