Can a goalkeeper be substituted?

Picture the moment properly: play has stopped, the ball is dead, and the goalkeeper walks off the pitch before his replacement is allowed to step on at the halfway line. That sequence is not a courtesy, it is the law.

Yes, a goalkeeper can be substituted. He is treated exactly like any outfield player for this purpose, same procedure, same stoppage-in-play requirement, same signal from the referee. IFAB's Laws of the Game, Law 3, spell out the mechanism: "The substitute only enters: during a stoppage in play at the halfway line after the player being replaced has left after receiving a signal from the referee." There is no separate, special goalkeeper clause for a normal, planned substitution. A keeper coming off for a fresh face at half-time or after a mistake follows the identical steps as a tired winger being withdrawn.

There is a second, stranger scenario worth picturing too, not a substitution at all, but a swap. Sometimes a team wants to switch a different player into goal without using up one of their substitutions: an outfield player takes the gloves, the old goalkeeper goes to play outfield, and nobody leaves the pitch. Law 3 covers this separately: "Any of the players may change places with the goalkeeper if: the referee is informed before the change is made the change is made during a stoppage in play." Note what is doing the work in that sentence, it says any of the players, not any substitute. This is a personnel swap between two people already on the field, and it needs the referee's advance knowledge, but it does not need a stoppage clock signal or a substitution slot. A captain gesturing to the fourth official during a break in play, then his goalkeeper and centre-back trading shirts, is this rule in action.

The edge case is the one nobody expects until it happens: a goalkeeper goes down injured, clearly unable to continue, and the team has already used every substitution available to them. There is no gloves-wearing specialist left to send on. Law 3 has an answer for this too, and it is blunt about it: "The team must have a goalkeeper, so one of the remaining players on the field takes over as goalkeeper and changes into a shirt that clearly distinguishes them from the other players and the match officials." A team cannot simply play on with ten outfield players and no goalkeeper because the rules run out of substitutes, someone has to zip into a spare kit, however unfamiliar the position, and stand between the posts. It is the reason clubs sometimes keep an old goalkeeper shirt in the kit bag even when their outfield subs bench looks nothing like an emergency squad.

What all three situations share is the same procedural backbone: inform the referee, wait for the stoppage, then act. Whether it is a routine change at half-time, a tactical swap mid-passage of play, or a crisis forced by injury and an empty bench, the Laws treat the goalkeeper's shirt as just another shirt that can move between bodies, as long as somebody is always wearing it.