The 2004–05 Euroleague was the fifth season of the professional basketball competition for elite clubs throughout Europe, organised by Euroleague Basketball Company, and it was the 48th season of the premier competition for European men's clubs overall. The 2004–05 season featured 24 competing teams, from 13 countries. The final of the competition was held in Olimpiisky Arena, Moscow, Russia, with the defending champions, Maccabi Tel Aviv, defeating Tau Cerámica by a score of 90-78.
The first phase was a regular season, in which the competing teams were drawn into three groups, each containing eight teams. Each team played every other team in its group at home and away, resulting in 14 games for each team in the first stage. The top 5 teams in each group and the best sixth-placed team advanced to the next round. The complete list of tiebreakers was provided in the lead-in to the Regular Season results.
If one or more clubs were level on won-lost record, tiebreakers were applied in the following order:
Head-to-head record in matches between the tied clubs
Overall point difference in games between the tied clubs
Overall point difference in all group matches (first tiebreaker if tied clubs were not in the same group)
Points scored in all group matches
Sum of quotients of points scored and points allowed in each group match
Key to colors
Top five places in each group, plus highest-ranked sixth-place team, advanced to Top 16
The surviving teams were divided into four groups of four teams each, and again a round robin system was adopted, resulting in 6 games each, with the two top teams advancing to the quarterfinals. Tiebreakers were identical to those used in the Regular Season.
The draw was held in accordance with Euroleague rules.
The teams were placed into four pools, as follows:
Level 1: The three group winners, plus the top-ranked second-place team
Each quarterfinal was a best-of-three series between a first-place team in the Top 16 and a second-place team from a different group, with the first-place team receiving home advantage.