The competition was won by Real Madrid, winners of the first five European Cups from 1956 to 1960, who beat Partizan 2–1 in a close final at Heysel Stadium in Brussels on 11 May 1966.

[1] Inter Milan were the defending champions, but were eliminated by eventual winners Real Madrid in the semi-finals.

In the preliminary round, Benfica recorded highest aggregate win in the history of the European Cup by beating Stade Dudelange 18–0 (8–0 away, 10–0 at home).

17 Nëntori, LASK, Levski Sofia, APOEL, Sparta Prague, HJK, Nantes, Keflavík, Derry City, Kilmarnock, Lausanne-Sports, and Werder Bremen made their debut in the competition.

Djurgårdens IF made their first appearance since the inaugural 1955–56 tournament, while Manchester United and Stade Dudelange returned to the competition after seven years.

They were leading 1. divisjon at the summer break on 1 July 1965, after 9 of 18 matches had been played, but finished second in autumn of 1965.

[3] Similar to previous editions, only title holders Inter Milan received a bye to the first round.

The remaining clubs would play the preliminary round in September and October, apart from two matches that took place in late August.

There were serious concerns regarding Brandywell Stadium state of the pitch, with IFA informing UEFA that it's not fit to host European Cup tie and ordering Derry City to play either at Windsor Park or Showgrounds, which club's board refusued to do.