The 1990–91 European Cup was the 36th season of the European Cup, a tournament for men's football clubs in nations affiliated to the Union of European Football Associations (UEFA). It was won for the first time by Red Star Belgrade on penalties in the final against Marseille; both were first-time finalists. This was only the second time that an Eastern European side had won the competition, after Steaua București of Romania in 1986. It was also the last tournament to be solely knock-out based, with a group stage added for the next season. Red Star won the tournament as the only Yugoslav club shortly before the breakup of Yugoslavia. This was also the last season to feature a team from East Germany, since the East and its West counterpart reunified in October 1990.

The 1990–91 season of the European Cup Winners' Cup was won by Manchester United against Barcelona. The victory for United was significant as it was the season English clubs returned to European football, after completing a five-year ban as a result of the Heysel Stadium disaster.