[2] Lyon were the defending champions and won the final against Barcelona 4–1, to win their sixth overall and fourth straight title.

[6] 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).

[7] A total of 60 teams from 48 associations entered the competition, with the entries confirmed by UEFA on 8 June 2018.

[68] The draw of the qualifying round was held at the UEFA headquarters in Nyon, Switzerland on 22 June 2018, 13:30 CEST.

[70][71] The teams were allocated into four seeding positions based on their UEFA club coefficients at the beginning of the season.

First, the 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.

As a result, two matches played by each second-placed team counts for the purposes of determining the ranking.

The draw for the round of 16 was held on 1 October 2018, 13:00 CEST, at the UEFA headquarters in Nyon, Switzerland.

This was after disorder was reported at Waterloo and Wimbledon Train stations and a bus carrying PSG supporters being searched and barred entry to Kingsmeadow Stadium.