The draw for the third qualifying round was held on 15 July 2011. The first legs were played on 26 and 27 July, and the second legs were played on 2 and 3 August 2011.
The third qualifying round was split into two separate sections: one for champions (called the Champions Route) and one for non-champions (called the League Route). The losing teams in both sections entered the play-off round of the 2011–12 UEFA Europa League.
The group stage features 32 teams, which were allocated into pots based on their 2011 UEFA club coefficients (except the title holders, Barcelona, who were placed in Pot 1 automatically), and then drawn into eight groups of four. Teams from the same association cannot be drawn against each other. The draw was held on 25 August 2011 in Monaco.
In each group, teams play against each other home-and-away in a round-robin format. The matchdays are 13–14 September, 27–28 September, 18–19 October, 1–2 November, 22–23 November, and 6–7 December 2011. The group winners and runners-up advanced to the round of 16, while the third-placed teams entered the round of 32 of the 2011–12 UEFA Europa League.
If two or more teams are equal on points on completion of the group matches, the following criteria are applied to determine the rankings (in descending order):
higher number of points obtained in the group matches played among the teams in question;
superior goal difference from the group matches played among the teams in question;
higher number of goals scored in the group matches played among the teams in question;
higher number of goals scored away from home in the group matches played among the teams in question;
If, after applying criteria 1) to 4) to several teams, two teams still have an equal ranking, the criteria 1) to 4) will be reapplied to determine the ranking of these teams;
superior goal difference from all group matches played;
higher number of goals scored from all group matches played;
higher number of coefficient points accumulated by the club in question, as well as its association, over the previous five seasons.
The 32 teams contain eleven former winners of the European Cup/Champions League (40 titles combined), and five teams (Manchester City, Napoli, Trabzonspor, Viktoria Plzeň and Oțelul Galați) which made their début appearance in the group stage. Eighteen UEFA member associations are represented in this group stage: England and Spain by four clubs, Italy, Germany and France by three, Russia and Portugal by two, while eleven associations are represented by one club, which are all domestic champions except Trabzonspor, which replaced Fenerbahçe due to match-fixing allegations.
Key to colours in group tables
Group winners and runners-up advance to the round of 16
The draw for the first knockout round was held on 16 December 2012 at UEFA headquarters in Nyon, Switzerland by UEFA General Secretary Gianni Infantino and UEFA Director of Competitions Giorgio Marchetti. The eight group winners, which play the second leg at home, were drawn against the eight group runners-up, with the restriction that teams from the same group or the same association cannot be drawn with each other. Starting with this season, the first knockout round matches will be held over four weeks, instead of the previous two weeks. The first legs will be played on 14, 15, 21 and 22 February, while the second legs will be played on 6, 7, 13 and 14 March 2012.