The 1999–2000 UEFA Champions League was the 45th season of the UEFA Champions League, UEFA's premier European club football tournament, and the eighth season since its rebranding from the "European Champion Clubs' Cup" or "European Cup". The competition was won by Real Madrid, who clinched a historic eighth title win by beating fellow La Liga side, Valencia in the final. The final was hosted in the Stade de France in Paris, the city where the original roots of the competition had begun nearly 50 years earlier.
The competition was dominated by the Spanish teams, with three of the four semi-finalists coming from Spain, namely Real Madrid, Valencia and Barcelona. The final between Real Madrid and Valencia marked the first time that both finalists in the competition had come from the same country.
The 1999–2000 edition of the Champions League sported a whole different format to the competition. An additional qualifying round was introduced to generate two group stages, firstly with 32 teams – eight groups of four – who played six matches each to reduce the competition to 16 teams for the second group stage, with the eight third-placed teams moving to the UEFA Cup third round. At the end of the second group stage, eight teams remained to contest the knock-out stage.
Location of teams of the 1999–2000 UEFA Champions League first group stage. Brown: Group A; Red: Group B; Orange: Group C; Yellow: Group D; Green: Group E; Blue: Group F; Purple: Group G; Pink: Group H.
16 winners from the third qualifying round, 10 champions from countries ranked 1–10, and six second-placed teams from countries ranked 1–6 were drawn into eight groups of four teams each. Compared to the two previous seasons, three associations (England, France, The Netherlands) were allowed three teams – the league winner and runner-up from each nation qualified for the first group stage, and the third-placed teams qualified for the third qualifying round – and three associations were allowed four teams (Germany, Italy, Spain) – the league winner and runner-up from each nation qualified for the first group stage, and the third- and fourth-placed teams qualified for the third qualifying round. Eight additional associations were still allowed two teams (Czech Republic, Greece, Norway, Portugal: league winner in group stage; Austria, Croatia, Denmark, Turkey, Russia: league winner in third qualifying round). The top two teams in each group advanced to the Champions League second group stage, while the third-placed teams advanced to round three of the UEFA Cup.
Eight winners and eight runners-up from the first group stage were drawn into four groups of four teams each, each containing two group winners and two runners-up. Teams from the same country or from the same first-round group could not be drawn together. The top two teams in each group advanced to the quarter-finals.