Rule 12 · Bunkers and putting greens
Rule 12: Bunkers
Official title: Bunkers
A bunker tests whether you can play the ball from sand. So you may touch the sand only within limits before your stroke. Loose things, though, you may remove.
12.1 When your ball is in a bunker
As soon as it touches sand inside the edge of the bunker, or lies there on ground where sand normally is. If it only lies on the lip or on grass and does not touch the sand, it is not in the bunker.
Rules question on this
12.2 Playing from a bunker
Since 2019 you may remove loose impediments and movable obstructions. You must not deliberately touch the sand to test it, or touch it with your club right in front of or behind your ball, in a practice swing or in your backswing. Putting down or leaning on a club is allowed. After your stroke you may rake, as long as it does not help your next stroke from the same bunker.
Rules questions on this
12.3 Relief in a bunker
There are separate Rules for this: Rule 16.1c for abnormal course conditions, Rule 16.2 for dangerous animals and Rule 19.3 for an unplayable ball.
Our own simplified summary of the 2023 Rules of Golf. The official Rules text is what counts.