Oppenheimer is a 2023 biographical film written, produced, and directed by Christopher Nolan. It follows the life of J. Robert Oppenheimer, the American theoretical physicist who helped develop the first nuclear weapons during World War II. Based on the 2005 biography American Prometheus by Kai Bird and Martin J. Sherwin, the film dramatizes Oppenheimer's studies, his direction of the Los Alamos Laboratory and his 1954 security hearing. Cillian Murphy stars as Oppenheimer, alongside Robert Downey Jr. as the United States Atomic Energy Commission member Lewis Strauss. The ensemble supporting cast includes Emily Blunt, Matt Damon, Florence Pugh, Josh Hartnett, Casey Affleck, Rami Malek, and Kenneth Branagh.

Oppenheimer was announced in September 2021. It was Nolan's first film not distributed by Warner Bros. Pictures since Memento (2000), due to his conflicts regarding the studio's simultaneous theatrical and HBO Max release schedule. Murphy was the first cast member to join, with the rest joining between November 2021 and April 2022. Pre-production began by January 2022, and filming took place from February to May. The cinematographer, Hoyte van Hoytema, used a combination of IMAX 65 mm and 65 mm large-format film, including, for the first time, scenes in IMAX black-and-white film photography. As with many of his previous films, Nolan used extensive practical effects, with minimal compositing.

Oppenheimer premiered at Le Grand Rex in Paris on July 11, 2023, and was theatrically released in the United States and the United Kingdom on July 21 by Universal Pictures. Its concurrent release with Warner Bros.'s Barbie was the catalyst of the "Barbenheimer" phenomenon, encouraging audiences to see both films as a double feature. Oppenheimer grossed over $976 million worldwide, becoming the third-highest-grossing film of 2023, the highest-grossing World War II-related film, the highest-grossing biographical film and the second-highest-grossing R-rated film at the time of its release.

The recipient of many accolades, Oppenheimer was nominated for leading thirteen categories at 96th Academy Awards, and won leading seven, including Best Picture, Best Director, Best Actor (Murphy), and Best Supporting Actor (Downey). It also won five Golden Globe Awards (including Best Motion Picture – Drama) and seven British Academy Film Awards (including Best Film), and was named one of the top ten films of 2023 by the National Board of Review and the American Film Institute. It has been named one of the greatest films of the 2020s and the 21st century.