What check means, and how to get out of it

Your king is attacked. That is all check is, and it is not a threat you may consider: the rules of chess do not contain a move that leaves your own king under attack, so answering it is the only thing you can do.

Three ways out
Not optional
No need to say it

A king is in check when an enemy piece attacks the square he is standing on. Nothing happens to him automatically. You simply have no legal move except one that ends the check, and if there is no such move the game is over and you have lost.

In check from a bishop

The bishop on b4 attacks e1 along the diagonal through c3 and d2. White is in check and has eight legal moves, every one of which is one of the three answers below.

The three ways out, and there is no fourth

Move the king. To a square nothing attacks. In the position above that is Kd1, Ke2, Kf1 or Kf2. Note that Kd2 is not on the list, because d2 is still on the bishop's diagonal.
Block the line. Put something in between. Here a knight can land on c3 or d2, and either one shuts the diagonal. Only works against a queen, rook or bishop, because you cannot block a knight or a pawn.
Capture the checker. Take the piece giving check, with anything, including the king if the piece is undefended. Here Nxb4 does it.

Those are the only three, and against a double check, where two pieces give check at once, only the first one is available. You cannot block two lines or capture two pieces in one move, so the king must move, and that is what makes double check so dangerous.

Things check is not

You do not have to say it. Announcing check is a courtesy in friendly games and is not part of the laws. In a tournament nobody says anything.
Check is not a threat you can ignore in order to make a bigger one. There is no counter-threat rule in chess.
A pinned piece cannot block or capture. If moving it would expose your king to a different attacker, it is not a legal move, however useful it looks.
The king cannot capture a defended piece to escape, because that is moving into check.
Check is not the goal. Beginners chase checks; the point is checkmate, and a check that achieves nothing usually just loses a tempo.

Why the check habit is worth building anyway

Not because giving check is good, but because looking at every check is how you find the tactics. Checks are forcing, there are rarely more than three or four of them in a position, and one of them is very often the move that wins. Scanning them costs a few seconds and catches almost every mate in one you would otherwise walk past.

It works defensively too. Before you move, look at every check your opponent has next turn. That one habit removes most blunders under 1200.

Black to move. Every check in this position, then the one that ends it.

Show the answer

52.g8=Q 52...d2#

The line ends in checkmate. The position is from a real game on Lichess, rated 595 in their puzzle pool, and it is one of the positions in the Mate in One skill in the trainer.

Questions people ask

Do you have to say check in chess?

No. It is not in the laws and strong players do not do it. Saying it in a friendly game is polite and harmless. In a rated game it is at best unnecessary and can be seen as distracting.

What happens if you do not get out of check?

You cannot fail to, because a move that leaves your king in check is not a legal move. If you play one over the board your opponent points it out and you take it back. If you have no legal move at all and you are in check, that is checkmate and you have lost the game.

Can you block a check with your king?

No, and you never need to. The king is the piece in check, so moving him out of the line is one of the three answers, but he cannot interpose himself in front of an attack on himself.

Can a king move next to another king to escape check?

No. Every square beside a king is attacked by that king, so moving next to him is moving into check, which is illegal whether or not you are currently being checked by something else.

Check sits under How a game ends in the reference. Nearby: