The 1998–99 UEFA Champions League was the 44th season of the UEFA Champions League, Europe's premier club football tournament, and the seventh since it was renamed from the "European Champion Clubs' Cup" or "European Cup". The competition was won by Manchester United, coming back from a goal down in the last two minutes of injury time to defeat Bayern Munich 2–1 in the final. Teddy Sheringham and Ole Gunnar Solskjær scored United's goals after Bayern had hit the post and the bar. They were the first English club to win Europe's premier club football tournament since 1984 and were also the first English club to reach a Champions League final since the Heysel Stadium disaster and the subsequent banning of English clubs from all UEFA competitions between 1985 and 1990. It was the first time since 1968 that Manchester United won the Champions League giving them their second title.

Manchester United also completed the Treble, becoming the fourth side in Europe to do so and in the process preventing Bayern Munich from achieving the feat themselves, Bayern eventually finished runners-up in their domestic cup two weeks later.

The Red Devils won the trophy without losing a single match, despite having competed in a group with Bayern Munich, Barcelona and Brøndby, plus two highly rated Italian clubs in the knock-out stages. However, United became champions with just five wins in total, the lowest number of wins recorded by a champion in the Champions League era to date, though the competition now has an extra round of two matches in the knock-out stages.

It was the first time the Champions League was won by a team that had neither won their domestic league nor the Champions League the previous season and therefore would not have qualified for the tournament under the old qualification rules (title holder or national league champion). For the second time, the runners-up of eight domestic leagues (three teams from Spain (including current UEFA Champions League title holder); two teams from England, France, Greece (replacing Turkey), the Netherlands, Germany, Italy and Portugal) were entered into the competition. The runners-up entered the second qualifying round while the league winners entered directly the group stage (except for Greece where both winner and runner-up entered the second qualifying).

Real Madrid were the defending champions, but were eliminated in the quarter-finals by Dynamo Kyiv.

56 teams entered the competition: the national champions of each of the top 48 nations in the UEFA coefficient rankings (except Liechtenstein), plus the runners-up from each of the top eight nations and UEFA Champions League holders, Real Madrid. The national champions of the associations ranked 1–7 (Italy, Germany, Spain, France, Netherlands, England and Portugal), plus the title holders, all received a bye to the group stage, while the national champions of the associations ranked 8–15 (Greece, Czech Republic, Norway, Austria, Russia, Croatia, Turkey and Denmark) and the runners-up of the associations ranked 1–8 all entered in the second qualifying round. The remaining national champions from the associations ranked 16–48 entered in the first qualifying round.^[1][2]

Losing teams qualified for the first round of the 1998–99 UEFA Cup.

Note: Winning teams of the first qualifying round were drawn against teams qualified directly for the second qualifying round (16 and 16 teams).

Twenty-four teams took part in the group stage: the national champions of Italy, Germany, Spain, France, Netherlands, England and Portugal, the title holders, and the 16 winning teams from the second qualifying round. Arsenal, Athletic Bilbao, Brøndby, Croatia Zagreb, HJK, Internazionale, Kaiserslautern, Lens and Sturm Graz made their debuts in the group stage of the competition. This was the first time that a team from Finland played in the group stage.

The teams were divided into six groups of four teams each, with the teams in each group playing each other twice (home and away) in a double round-robin format. Three points were awarded for each win, with one point each for a draw and none for a defeat. The winners of each group progressed to the quarter-finals, along with the two best second-placed teams. In the event that two or more teams had the same number of points at the end of the group stage, the rankings of the teams in question were determined by the following criteria:^[3]

The two best runners-up were determined by the following criteria:^[4]

The knockout stage was played in a single-elimination tournament format consisting of three rounds: quarter-finals, semi-finals and final. Each tie in the quarter-finals and semi-finals was played over two legs, with each team playing one leg at home, while the final was played as a single match at a neutral venue. In the quarter-finals and semi-finals, in the event that two teams scored the same number of goals over the two legs of their tie, the winner would be determined by the number of goals scored away from home. If both sides scored the same number of goals away from home, two 15-minute periods of extra time would be played. If both teams scored the same number of goals during extra time, the visiting team would qualify for the next round by virtue of having scored more goals away from home. If neither side scored during extra time, the match would be decided by a penalty shoot-out. In the final, if the scores were level after 90 minutes, two 15-minute periods of golden goal extra time would be played; i.e. whichever team scored first would be declared the winner. If neither side scored during golden goal extra time, a penalty shoot-out would again be used to determine the winner.^[4]

In the quarter-finals, the two best runners-up could not be drawn together, nor could the winners and runners-up from the same group. Both runners-up played the first leg of their quarter-final at home, as did the teams drawn first in the other two quarter-finals.^[4]

The top scorers from the 1998–99 UEFA Champions League (excluding qualifying rounds) are as follows: