A match is played by two teams, each consisting of not more than eleven players, one of whom is the goalkeeper. A match may not start if either team consists of fewer than seven players.

Up to a maximum of three substitutes may be used in any match played in an official competition organised under the auspices of FIFA, the confederations or the national associations.

The rules of the competition must state how many substitutes may be nominated, from three up to a maximum of seven.

In other matches, substitutes may be used provided that:

the teams concerned reach agreement on a maximum number
the referee is informed before the match. If the referee is not informed, or if no agreement is reached before the start of the match, no more than three substitutes are allowed.

In all matches the names of the substitutes must be given to the referee prior to the start of the match. Substitutes not so named may not take part in the match.

To replace a player by a substitute, the following conditions must be observed:

the referee is informed before any proposed substitution is made
a substitute only enters the field of play after the player being replaced has left and after receiving a signal from the referee a substitute only enters the field of play at the halfway line and during a stoppage in the match a substitution is completed when a substitute enters the field of play from that moment, the substitute becomes a player and the player he has replaced ceases to be a player a player who has been replaced takes no further part in the match all substitutes are subject to the authority and jurisdiction of the referee, whether called upon to play or not

Any of the other players may change places with the goalkeeper, provided that:

the referee is informed before the change is made
the change is made during a stoppage in the match
Infringements/Sanctions

If a substitute enters the field of play without the referees permission:

play is stopped
the substitute is cautioned, shown the yellow card and required to leave the field of play
play is restarted with a dropped ball at the place it was located when play was stopped

If a player changes places with the goalkeeper without the referees permission before the change is made:

play continues
the players concerned are cautioned and shown the yellow card when the ball is next out of play
For any other infringements of this Law:

the players concerned are cautioned and shown the yellow card
Restart of Play

If play is stopped by the referee to administer a caution:

the match is restarted by an indirect free kick, to be taken by a player of the opposing team from the place where the ball was located when play was stopped
Players and Substitutes Sent Off

A player who has been sent off before the kick-off may be replaced only by one of the named substitutes.

A named substitute who has been sent off, either before the kick-off or after play has started, may not be replaced.