The nervous schoolteacher Colin, observing the sexual revolution in London, has little personal sexual experience and wishes to gain "the knack", a way to seduce women. He turns to a friend, an aggressive, womanizing drummer known only by his surname, Tolen. Tolen gives him unhelpful advice to consume more protein and use intuition, acknowledging intuition is not something that can be completely learned, and espouses the importance of domination. He then suggests Colin move into his residence, where he and another friend "share" women. Colin also becomes determined to obtain a larger bed.
While Colin works on his new living arrangements, a young virginal woman named Nancy arrives to London from out of town, searching for the YWCA. She stops by a clothing store and is won over by the flattery of the clerk, until she overhears him repeating the same words to every female customer. While still seeking the YWCA and asking strangers for directions, she sees Colin purchasing a large cast iron bed. She helps Colin and his friends bring the bed to their residence. There, Tolen makes sexual advances on her, and gives her an unwanted kiss, though telling her she will not be "raped" without consent.
In a public space, Tolen pursues Nancy again, and she faints. When she wakes up, she begins claiming she was raped, though this was not the case. Tolen, Colin and their friends find themselves unable to restrain her from loudly repeating the allegations, or slashing the tires of Tolen's motorcycle, and she runs back to the residence, where she breaks Tolen's records and strips naked. The men become convinced her rape allegations reflect fantasy and urge Tolen to have sex with her. When Nancy emerges from the room wearing a robe, she instead expresses more attraction to Colin, and he returns the interest. Some time later, there is gossip that Nancy and Colin will be co-habitating.
After seeing Ann Jellicoe's play The Knack, the producers envisioned a film adaptation. They offered the position of director to Lindsay Anderson, who refused.
Having worked with The Beatles on A Hard Day's Night, Lester was another candidate for director, and agreed to take the position. Lester made major changes to the play, adding his own touch through direct address, unexpected oddly-edited sequences, humorous subtitles, and a Greek chorus of disapproving members of "the older generation." Filming took place in a few weeks, and Lester employed television advertising techniques. Talking about the film in the 1980s, actor Ray Brooks said:
Lester himself makes a brief cameo as an annoyed bystander. John Barry contributed the jazzy score, which features a memorable organ solo by Alan Haven. Jane Birkin, Charlotte Rampling, and Jacqueline Bisset all made their first cinematic appearances in the film as extras, together with Top of the Pops disc girl Samantha Juste.
In The New York Times, Bosley Crowther positively reviewed it as "delightfully mobile" and a "frenziedly running, jumping picture". Variety staff praised the performances, citing Rita Tushingham as perfect in her role.
In 2016, The Hollywood Reporter ranked it the 49th best film to win the Palme d'Or, saying it "hasn't aged well" but the setting was a great asset. In 2001, the Wallflower Critical Guide noted the creativity in cinematography and editing, but said it disrupted the storytelling.
The film was entered into competition at the 1965 Cannes Film Festival, where it won the Palme d'Or.