The 2005–06 UEFA Champions League group stage matches took place between 13 September and 7 December 2005.
Seeding was determined by the UEFA coefficients. Clubs from the same association were paired up to split the matchdays between Tuesday and Wednesday. Clubs with the same pairing letter would play on different days, ensuring that teams from the same city (e.g. Milan and Internazionale, who also share a stadium) did not play on the same day.
Based on paragraph 4.05 in the UEFA regulations for the current season, if two or more teams are equal on points on completion of the group matches, the following criteria are applied to determine the rankings:
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 away from home in the group matches played among the teams in question;
superior goal difference from all group matches played;
higher number of goals scored in 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.