A group stage (also known as pool play or the pool stage) is the round-robin stage of many sporting championships, particularly a sports' World Cup. The name implies that there is also a knock out stage to follow. For example in both the FIFA World Cup and Rugby World Cup the teams are split into groups (also known as pools) where they play each team in their group once under a round robin system. Points are earned during group play in order to rank the teams within a group. The top ranked teams (often the top two) from each group then proceed to the tournament's knock out phase. From there the tournament continues under a knock out system until the winner is found.

Group stage usually consists of four teams where the two teams with the most points qualify. If points are level the top 2 teams would be decided on goal difference. If goal difference is level, then it goes onto goals scored.

In international competition and some club competitions, group play consists of a single match against each opponent in the group. In other club competitions, such as the UEFA Champions League, each club has two matches - one home and one away - against each opponent.