[2] The qualifying competition consists of three rounds:[3] In the preliminary round and main round, teams are ranked according to points (3 points for a win, 1 point for a draw, 0 points for a loss), and if tied on points, the following tiebreaking criteria are applied, in the order given, to determine the rankings (Regulations Articles 14.01 and 14.02):[3] To determine the best third-placed team from the main round, the following criteria are applied (Regulations Article 15.01):[3] In the play-offs, the team that scores more goals on aggregate over the two legs qualifies for the final tournament.

If no goals are scored during extra time, the tie is decided by penalty shoot-out (Regulations Article 20.01).

[5][6] The mechanism of the draws for each round was as follows: Based on the decisions taken by the UEFA Emergency Panel, Azerbaijan/Armenia, Spain/Gibraltar, Kosovo/Serbia, and Kosovo/Bosnia and Herzegovina would not be drawn into the same group.

The draw for the play-offs was held on 6 July 2017, 13:30 CEST, at the UEFA headquarters in Nyon, Switzerland.

[7][8] There were no seedings, with the only restriction that the best third-placed team (Poland) could not be drawn against the runner-up from the same main round group (Serbia).