A Momentary Lapse of Reason is the thirteenth studio album by the English progressive rock band Pink Floyd, released in the UK on 7 September 1987 by EMI and the following day in the US on Columbia. It was recorded primarily on the converted houseboat Astoria, belonging to the guitarist, David Gilmour.

A Momentary Lapse of Reason was the first Pink Floyd album recorded without the founding member Roger Waters, who departed in 1985. The production was marred by legal fights over the rights to the Pink Floyd name, which were not resolved until several months after release. It also saw the return of the keyboardist and founding member Richard Wright, who was fired by Waters during the recording of The Wall (1979), as a session player.

Unlike Pink Floyd's preceding studio records, A Momentary Lapse of Reason is not a concept album. It includes writing contributions from outside songwriters, following Gilmour's decision to include material once intended for his third solo album. The album was promoted with three singles: the double A-side "Learning to Fly" / "Terminal Frost", "On the Turning Away", and "One Slip".

A Momentary Lapse of Reason received mixed reviews; some critics praised the production and instrumentation but criticised Gilmour's songwriting, and it was derided by Waters. It reached number three in the UK and US, and outsold Pink Floyd's previous album, The Final Cut (1983). It was supported by a successful world tour between 1987 and 1989, including a free performance on a barge floating on the Grand Canal in Venice, Italy.