The 2005–06 Euroleague was the 6th season of the professional basketball competition for elite clubs throughout Europe, organised by Euroleague Basketball Company, and it was the 49th season of the premier competition for European men's clubs overall.
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
3–5 are used to break ties between 6th place teams
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 Top 16 group included one team from each pool. The draw was conducted under the following restrictions:
No more than two teams from the same Regular Season group could be placed in the same Top 16 group.
No more than two teams from the same country could be placed in the same Top 16 group.
If there was a conflict between these two restrictions, (1) would receive priority.
Another draw was held to determine the order of fixtures. In the case of two teams from the same city in the Top 16 (Panathinaikos and Olympiacos, Efes Pilsen and Ülker) they were scheduled so that every week, only one team would be at home.
Key to colors
Top two places in each group advanced to quarterfinals
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.
