Castling in Chess
The only move in chess where two pieces move at once, used to protect your king and activate your rook.
Published 2026-02-01 | Last verified 2026-02-17
Professor Archer says: I tell every student the same thing on day one: learn to castle early. In my first year of playing chess, I lost more games to a king stuck in the center than to any other single cause. Castling is like locking the front door of your house. It does not guarantee safety, but without it, you are inviting trouble.
How Castling Works
Castling is unique in chess because it is the only legal move where two pieces move in a single turn. The king slides two squares toward one of its rooks, and that rook leaps over the king to land on the square the king crossed. Despite involving two pieces, this counts as one move and uses only the king's turn.
There are two types of castling. Kingside castling (written O-O in chess notation) moves the king from e1 to g1, with the rook going from h1 to f1. Queenside castling (written O-O-O) moves the king from e1 to c1, with the rook going from a1 to d1. For Black, the same applies on the eighth rank: the king goes from e8 to g8 or c8.
Kingside castling is more common because it requires clearing only two pieces (the knight and bishop), whereas queenside castling requires clearing three (the queen, bishop, and knight). Kingside castling also tends to tuck the king into a safer corner, since the pawns on f2, g2, and h2 form a natural shelter.
The mechanical action is simple: pick up the king, place it two squares toward the rook, then move the rook to the other side. In tournament play, you must touch the king first. If you touch the rook first, you may be required to make a rook move instead.
Before Castling: Starting Position
This diagram shows the position just before White can castle. The king sits on e1 and both rooks are on their starting squares. The squares between the king and the h1 rook are clear, so kingside castling is available.
White is ready to castle kingside. The king on e1 will move to g1, and the rook on h1 will jump to f1.
After Kingside Castling (O-O)
After kingside castling, the king is safely tucked on g1 behind the f2, g2, and h2 pawns. The rook has moved from h1 to f1, where it is more active and connected to the rest of the position. This is the most common type of castling and the one you will use in the majority of your games.
After O-O: king on g1, rook on f1. The king is sheltered behind three pawns.
After Queenside Castling (O-O-O)
Queenside castling places the king on c1 and the rook on d1. The rook immediately occupies the central d-file, which is often open or semi-open. The trade-off is that the king on c1 can be slightly more exposed, since the a-pawn is farther away and the b-pawn can become a target. Queenside castling is less common but can be a strong choice in positions where the kingside is under pressure.
After O-O-O: king on c1, rook on d1. The rook is centralized but the king is slightly more exposed.
How to Castle Step by Step
- Clear the pieces between king and rook - Develop your knights and bishops so that no pieces remain between your king and the rook you want to castle with. For kingside castling, move the knight and bishop off the f1 and g1 squares. For queenside, clear the queen, bishop, and knight from b1, c1, and d1.
- Verify castling conditions - Confirm that neither the king nor the rook has previously moved, the king is not in check, and the king will not pass through or land on a square attacked by an enemy piece.
- Move the king two squares toward the rook - Pick up the king and move it two squares toward the rook. For kingside castling, the king goes from e1 to g1. For queenside, from e1 to c1. Always touch the king first in tournament play.
- Move the rook to the other side of the king - Place the rook on the square the king crossed. For kingside, the rook goes from h1 to f1. For queenside, from a1 to d1. The entire sequence counts as a single move.
Castling Requirements
Castling comes with a specific set of requirements, and every single one must be met. If any condition is violated, the castling move is illegal.
First, neither the king nor the rook involved may have previously moved. If your king moved to e2 and then back to e1, you have still lost castling rights because the king moved. The same applies to the rook. This is why experienced players sometimes delay moving the king or rooks early in the game, to preserve the option to castle.
Second, all the squares between the king and the rook must be empty. You cannot castle through your own pieces or through enemy pieces. This means you need to develop your bishops and knights before you can castle.
Third, the king must not currently be in check. You cannot castle as a way to escape check. However, the rook may be under attack. There is no rule preventing the rook from being threatened.
Fourth, the king must not pass through any square that is attacked by an enemy piece. The king travels through two squares (one intermediate, one destination), and neither can be under attack. However, the rook can pass through an attacked square. This restriction only applies to the king.
Fifth, the king must not end up on a square that is in check. This is really just the standard rule that you can never move your king into check.
Kingside vs Queenside Castling
The position below shows both White and Black with full castling rights. Let us compare the two options.
Kingside castling (O-O) tucks the king into the corner behind the f, g, and h pawns. This is generally the safer option because the king ends up behind three undisturbed pawns, and it takes fewer preparatory moves since only the knight and bishop need to be developed first.
Queenside castling (O-O-O) places the king on c1 (or c8 for Black) and the rook on d1. The rook immediately occupies the central d-file, which can be an advantage. However, the king on c1 is slightly more exposed because the a-pawn may be undefended and the b-pawn can be targeted.
In practice, the choice depends on your opening and your opponent's setup. If your opponent has launched a kingside attack, castling queenside might be wiser. If the center is closed and the queenside looks dangerous, kingside is likely better. The ability to read the position and choose the right side is a hallmark of improving players.
Both sides can castle kingside (O-O) or queenside (O-O-O). Note the clear squares between king and rooks.
When Castling Is Blocked
In this position, White cannot castle kingside because the Black bishop on b4 attacks the f1 square, which the king must pass through. The king cannot move through check, so kingside castling is temporarily illegal. White would need to deal with the bishop first, or consider castling queenside instead.
Remember: it is not enough for the destination square to be safe. Every square the king touches during castling must be free from attack.
White cannot castle kingside because the bishop on b4 attacks f1, a square the king must cross.
Castling Notation
In standard algebraic notation, castling uses the letter O (not the number zero). Kingside castling is written as O-O, and queenside castling is written as O-O-O. The number of Os corresponds to the side of the board: two for the shorter kingside, three for the longer queenside.
Here is an example from a typical Italian Game opening: 1. e4 e5 2. Nf3 Nc6 3. Bc4 Bc5 4. O-O. In this sequence, White castles kingside on move four after developing the knight and bishop.
Some older texts and informal usage may write castling as 0-0 or 0-0-0 using zeros, but the official standard (used by FIDE and most publications) is the letter O. When recording your games, using the correct notation helps avoid confusion.
When to Castle and When Not To
The general advice for beginners is straightforward: castle early. In most games, castling within the first ten moves is ideal. This gets your king out of the center, where it is vulnerable to tactical strikes, and connects your rooks so they can work together on the back rank.
However, there are situations where delaying or even forgoing castling is correct. In some openings, the center is locked and there is no immediate danger to the king, so you might use those tempi for other purposes. In certain sharp positions, castling into an opponent's attack can be disastrous. If your opponent has already advanced pawns toward your intended castling side, you may be castling into danger rather than away from it.
The key question to ask is always: "Is my king safer after castling than before?" If the answer is yes, castle. If your opponent has aimed a battery of pieces at your kingside, consider castling queenside or keeping the king in the center temporarily while you address the threats.
Opposite-Side Castling
Opposite-side castling occurs when one player castles kingside and the other castles queenside. These games tend to be sharp and tactical, as both players launch pawn storms against the other's king. The pawns in front of your own king serve as shelter, while the pawns on the opposite side become battering rams.
In opposite-side castling positions, speed is everything. The first player to open lines against the enemy king often gains a decisive attack. This is why these positions require careful calculation and an understanding of when to push pawns aggressively versus when to slow down and shore up your own defenses.
You will commonly see opposite-side castling in the Sicilian Defense and other sharp openings where both sides are fighting for the initiative.
Frequently Asked Questions
What is castling in chess?
Castling is a special move where the king moves two squares toward a rook, and that rook jumps over the king to the adjacent square. It is the only move in chess where two pieces move at the same time, and it serves to improve king safety while activating the rook.
How do you castle in a game?
To castle, ensure that neither the king nor the chosen rook has previously moved, all squares between them are empty, and the king is not in check, does not pass through check, and does not land in check. Then move the king two squares toward the rook and place the rook on the other side.
Why is castling important?
Castling is important because it tucks the king behind a wall of pawns for safety and connects the rooks so they can work together on the back rank. Most games are lost when the king remains in the center too long, making early castling a cornerstone of sound play.
Can you castle after moving your king?
No. Once the king has moved, you permanently lose castling rights on both sides, even if the king returns to its starting square. This is why experienced players avoid moving the king early in the game unless absolutely necessary.
Can you castle out of check?
No. You cannot castle while your king is in check. You must first escape the check by moving the king, blocking the attack, or capturing the attacking piece. Once the check is resolved, you may castle on a future turn if all other conditions are still met.
Can you castle if your rook is under attack?
Yes. The rook being attacked does not prevent castling. Only the king has restrictions about attacked squares. The king cannot be in check, cannot pass through check, and cannot land in check, but the rook faces no such limitations.
Can you castle on both sides in one game?
No. In a single game, you can only castle once. However, you can choose either kingside castling (O-O) or queenside castling (O-O-O) as long as the conditions are met for that side.
What is the difference between kingside and queenside castling?
Kingside castling (O-O) moves the king to g1 behind three pawns for safety. It requires clearing only two pieces and is more common. Queenside castling (O-O-O) moves the king to c1 with the rook landing on the active d-file, but the king is slightly more exposed. Queenside castling requires clearing three pieces.
Professor Archer says: One thing I have learned after twenty years of teaching: the students who castle consistently outperform those who "forget" or delay it. Make it a habit. Get your king safe, get your rooks connected. The rest of your plan can flow from there.
Quick Quiz
Which of the following would prevent you from castling?
- Your rook is being attacked by an enemy piece - The rook being attacked does not prevent castling. Only the king has restrictions about passing through or landing on attacked squares.
- Your king previously moved to e2 and then moved back to e1 (Correct) - Correct. Once the king has moved, you permanently lose castling rights, even if the king returns to its original square.
- Your opponent just castled on the previous move - Both sides can castle independently. Your opponent castling has no effect on your own castling rights.
- It is move thirty of the game - There is no time limit on castling. As long as all the requirements are met, you can castle at any point in the game.