6 per side: 5 field players + 1 goalkeeper; Roster: 12 players per game (6 on field, 6 substitutes); unlimited substitutions on-the-fly; Officials: 3-person crew (referee + 2 umpires) at international/Olympic level
Why people argue about this
People often assume that the goalkeeper is one of those 12-player maximums, leading to arguments about whether a team can bring in an extra player just for goalkeeping purposes. Actually, the goalkeeper counts as part of the 5 field players allowed per side, so there's no room for another keeper even if you wanted to add one.