The 2003–04 UEFA Champions League was the 12th season of UEFA's premier European club football tournament, the UEFA Champions League, since its rebranding from the European Cup in 1992, and the 49th tournament overall. The competition was won by Portugal's Porto, who defeated Monaco of France 3–0 at the Arena AufSchalke in Gelsenkirchen, Germany for Portugal's first win since 1987. This was Porto's second European trophy in two years, following their UEFA Cup success from the previous season. This was the first UEFA Champions League competition to feature a 16-team knockout round instead of a second group stage.
A total of 72 teams from 48 UEFA member associations participated in the 2003–04 UEFA Champions League. Liechtenstein (who don't have their own domestic league) as well as Andorra and San Marino are not participating. Also wasn't admitted Azerbaijan, which was suspended by UEFA. Each association enters a certain number of clubs to the Champions League based on its league coefficient; associations with a higher league coefficients may enter more clubs than associations with a lower league coefficient, but no association may enter more than four teams.
Associations 1–3 each have four teams qualify.
Associations 4–6 each have three teams qualify.
Associations 7–15 each have two teams qualify.
Associations 16–52 (except Azerbaijan, Liechtenstein, Andorra and San Marino) each have one team qualify.
For the 2003–04 UEFA Champions League, the associations are allocated places according to their 2002 UEFA country coefficients, which takes into account their performance in European competitions from 1997–98 to 2001–02.
Since the title holders (Milan) also qualified for the Champions League Third qualifying round through their domestic league, one Third qualifying round spot was vacated. Due to this, as well as due to suspension of Azerbaijan, the following changes to the default access list are made:
The champions of association 16 (Switzerland) are promoted from the second qualifying round to the third qualifying round.
The champions of associations 26, 27 and 28 (Romania, Hungary and Slovenia) are promoted from the first qualifying round to the second qualifying round.
Teams entering in this round
Teams advancing from previous round
First qualifying round (20 teams)
20 champions from associations 29–52 (except Azerbaijan, Liechtenstein, Andorra and San Marino)
Second qualifying round (28 teams)
12 champions from associations 17–28
6 runners-up from associations 10–15
10 winners from the first qualifying round
Third qualifying round (32 teams)
7 champions from associations 10–16
3 runners-up from associations 7–9
5 third-place finishers from associations 1–6 (except Italy)
Azerbaijan (AZE): Clubs from Azerbaijan were not admitted to UEFA competitions as no domestic league took place in 2002–03 season and AFFA was suspended by UEFA as a result of ongoing conflict between the clubs and federation.
Location of teams of the 2003–04 UEFA Champions League group stage. Brown: Group A; Red: Group B; Orange: Group C; Yellow: Group D; Green: Group E; Blue: Group F; Purple: Group G; Pink: Group H.
Title holders, 16 winners from the third qualifying round, 9 champions from countries ranked 1–10, and six second-placed teams from countries ranked 1–6 were drawn into eight groups of four teams each. The top two teams in each group advanced to the Champions League play-offs, while the third-placed teams advanced to the Third Round of the UEFA Cup.
Tiebreakers, if necessary, were applied in the following order:
Points earned in head-to-head matches between the tied teams.
Total goals scored in head-to-head matches between the tied teams.
Away goals scored in head-to-head matches between the tied teams.
Real Sociedad, Celta Vigo, Stuttgart and Partizan made their debut appearance in the group stage. This season became the first in the history of the Champions League in which three Greek clubs will play in the group stage