A single-elimination tournament — also called an Olympic system tournament, a knockout (or, knock-out), single penetration, or sudden death tournament — is a type of elimination tournament where the loser of each bracket is immediately eliminated from winning the championship or first prize in the event.

This does not always mean that the defeated competitor will not participate further in the tournament; in some such tournaments, consolation or "classification" contests are subsequently held among those already defeated to determine the awarding of lesser places, for example, a third place playoff. Where more than two competitors can play in each match, such as in a shootout poker tournament, players are removed when they can no longer play until one player remains from the group. This player moves on to the next round.

Some competitions are held with a pure single-elimination tournament system. Others have many phases, with the last being a single-elimination final stage called playoffs.