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Competition format

Held every two years, the UEFA European Under-21 Championship consists of a qualifying group stage, play-offs and, from 2017, a 12-team final tournament.
 

Competition format

Held every two years, the UEFA European Under-21 Championship consists of a qualifying group stage, play-offs and, from 2017, a 12-team final tournament.

Qualifying is open to all UEFA member associations. Teams initially compete in a qualifying group stage, with the nine section winners automatically joining the hosts – Poland – in the finals and the four best runners-up playing off for the remaining two places.

The final tournament, expanded to 12 teams (from eight) for 2017, consists of three groups of four. Sides play each other once, with the winners and the best runner-up from the three pools advancing to the semi-finals, where it becomes a knockout competition. In finals held a year before a summer Olympic Games (e.g. 2015, 2019), the championship also serves as a qualification event for the Olympic Football Tournament.

Regulations
The Regulations of the UEFA European Under-21 Championship are initially drawn up by the UEFA administration before being submitted to the UEFA National Team Competitions Committee. They are then forwarded upon that committee's approval to the UEFA Executive Committee for ratification.

Players are eligible for the 2017 UEFA European Under-21 Championship if they were born on, or after, 1 January 1994.

http://www.uefa.com/under21/season=2017/competitionformat/index.html#competition+format