Bob and Carol Sanders (Culp and Wood) are a married upper-middle-class couple with a little too much time on their hands. After going to a group therapy retreat, Bob and Carol start to explore a new openness in their relationship. Bob confesses a one-night stand with a casual acquaintance. Carol not only isn't mad, she's turned on, and soon enough she has her own fling, which she tells Bob about.
Their close friends Ted and Alice Henderson (Gould and Cannon) are shocked and uncomfortable when Bob and Carol tell them about their new open relationship. However, after Alice has a breakthrough in therapy, she apologizes to Carol for being uptight. A joint vacation to Las Vegas then threatens to become a polyamorous weekend pairing up Ted and Carol and Alice and Bob.
Gould and Cannon earned Academy Award nominations for their performances, as did Mazursky and Larry Tucker for their original screenplay and Charles Lang for his cinematography. Quincy Jones composed the music.
- Bikini Bar: The gang goes to a nightclub that features women dancing on a stage in flimsy outfits.
- Bland-Name Product: The goofy retreat where naked people are walking around and Bob and Carol go to a weird group therapy session is called "the Institute", but it's obviously the Esalen Institute, which first started getting famous in the late 1960s for its New Age group therapy sessions.note
- Breaking the Fourth Wall: Bob looks straight into the camera while nuzzling Alice. The would-be orgy grinds to a halt immediately after.
- Call-Back: The film ends with our heroes leaving the casino along with quite a few other hotel guests. They stand around the front entrance, and it becomes clear that they're having a staring therapy session like in the opening scenes at Esalen.
- The Cameo: Bill Cosby, Robert Culp's co-star in I Spy, bumps into Bob at a nightclub.
- Ethical Slut: Carol becomes this after finding out about Bob's affair. She brings a man home for sex and then criticizes Bob when he gets uptight about it.
- Fanservice Extra: All the lovely naked ladies strolling around the Esalen Institute.
- Lingerie Scene: Carol and Alice in their underwear in more than one scene.
- Multi-Character Title: Bob & Carol & Ted & Alice
- My Girl Is a Slut: Gender-flipped. When Bob confesses his infidelity, not only is Carol not mad, she's turned on. Sex on the floor follows.
- A Party, Also Known as an Orgy: The party in the hotel suite nearly becomes this, after Alice finds out about Ted's affair and demands an orgy.
- Polyamory: The two couples seem ready to explore this at the end, but they change their minds.
- Really Gets Around: One of the attendees at the therapy session along with Bob and Carol says that her problem is "I can't say no to any man."
- Sexy Shirt Switch: Carol is wearing nothing but her husband's shirt when Bob comes home early and finds her with a man in the house.
- The Shrink: Alice has a breakthrough at her regular therapy session.
- Title Drop: "Here's a toast to Bob and Carol and Ted and Alice."
- We Are as Mayflies: Part of Bob's argument when he urges Ted to act on his impulses and have an affair.Bob: Do you realize you're here for about ten seconds?