[5] The format of the competition remained unchanged from previous years, starting from the qualifying round (played as mini-tournaments with four teams in each group), followed by the knockout phase starting from the round of 32 (played as home-and-away two-legged ties except for the one-match final).

The champions of Armenia (Yerevan LH), Azerbaijan (Gabala) and Gibraltar (Lincoln Red Imps) did not enter.

[48] The draw of the qualifying round was held on 23 June 2017, 13:30 CEST, at the UEFA headquarters in Nyon, Switzerland.

[51][52] The 40 teams were allocated into four seeding positions based on their UEFA club coefficients at the beginning of the season.

First, the ten teams which were pre-selected as hosts were drawn from their own designated pot and allocated to their respective group as per their seeding positions.

In the knockout phase, teams played against each other over two legs on a home-and-away basis, except for the one-match final.

If the aggregate score was tied after full time of the second leg, the away goals rule was used to decide the winners.

The draw for the round of 16 was held on 16 October 2017, 13:30 CEST, at the UEFA headquarters in Nyon, Switzerland.

The draw for the quarter-finals was held on 24 November 2017, 13:30 CET, at the UEFA headquarters in Nyon, Switzerland.