Last Year at Marienbad (French: L'Année dernière à Marienbad), released in the United Kingdom as Last Year in Marienbad, is a 1961 French New Wave avant-garde psychological drama film directed by Alain Resnais and written by Alain Robbe-Grillet.

Set in a palace in a park that has been converted into a luxury hotel, the film stars Delphine Seyrig and Giorgio Albertazzi as a woman and a man who may have met the year before and may have contemplated or begun an affair, with Sacha Pitoëff as a second man who may be the woman's husband. The characters are unnamed.

In an ornate baroque hotel populated by wealthy individuals and couples who socialize with one another, a man approaches a woman and claims they met the previous year at a similar resort (possibly Frederiksbad, Karlstadt, Marienbad, or Baden-Salsa) and had an affair. He asserts that she responded to his request to run away together by asking him to wait a year. The woman, however, insists she has never met the man. He attempts to remind her of their shared past, while she rebuffs him and contradicts his accounts. Between interactions with the woman, a second man, who may be her husband, asserts his dominance over the first by repeatedly defeating him in a game of Nim.

Through ambiguous flashbacks and disorienting shifts in time and location, the film explores the relationships among the three characters. Conversations and events are repeated in different parts of the building and grounds, accompanied by numerous tracking shots of the hotel's corridors with ambiguous and repetitive voice-overs. The film offers no definitive conclusion regarding what is real and what is imagined, but by the end, the woman relents and leaves the hotel with the first man.

Although the characters are unnamed in the film, in Robbe-Grillet's published "ciné-novel" of the screenplay, the first man is referred to as "X," the woman as "A," and the second man as "M."

Last Year at Marienbad was created out of an unusual collaboration between writer Alain Robbe-Grillet and director Alain Resnais. Robbe-Grillet described its basis:

Alain Resnais and I were able to collaborate only because we saw the film in the same way from the start; and not just in the same general outlines but exactly, in the construction of the least detail as in its total architecture. What I wrote might have been what was already in his mind; what he added during the shooting was what I might have written. ... [P]aradoxically enough, and thanks to this perfect identity of our conceptions, we almost always worked separately.

The screenplay Robbe-Grillet wrote was very detailed, specifying not only the dialogue and gestures and décor, but also the placement and movement of the camera and the sequencing of shots in the editing. Resnais filmed the script with great fidelity, and when Robbe-Grillet, who was not present during the filming, saw the rough cut, he said he found the film just as he had intended it, while recognizing how much Resnais had added to make it work on the screen and fill out what was absent from the script. Robbe-Grillet published his screenplay, illustrated by shots from the film, calling it a "ciné-roman" (ciné-novel).