The 1999–2000 UEFA Champions League first group stage matches took place between 14 September and 3 November 1999.
The draw for the group stage was made in August 1999.
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.
Notes Based on Article 7.06 in the UEFA regulations, if two or more teams are equal on points on completion of the group matches, the following criteria will be applied to determine the rankings: