Pokémon: The First Movie - Mewtwo Strikes Back is a 1998 Japanese anime fantasy adventure film directed by Kunihiko Yuyama. It is the first theatrical release in the Pokémon franchise. The film was first released in Japan on July 18, 1998. On July 8, 1999, an extended version of the film aired on Japanese television. In addition to an added prologue, the updated version included new animation and CGI graphics. The film primarily consists of two segments: Origin of Mewtwo, the 10-minute prologue added to the extended version of the film; and Mewtwo Strikes Back, the main 75-minute film feature. Overseas, the prologue can only be seen as a bonus short in DVD versions of Pokémon: Mewtwo Returns. The events of the film take place during the first season of Pokémon: Indigo League. The English-language adaptation was released in North America and other countries on November 10, 1999, by Warner Bros. Pictures.

In Japan, the film received positive reviews, with praise directed at the film's emotional impact and exploration of ethical topics such as cloning, genetic modification, and existentialism. However, the English-language version received generally negative reviews from film critics, with much of the criticism pointed at the poorly dubbed voice acting and its inclusion of an anti-violence message despite the overall concept of the series. Further, retrospective criticism of the English-language version has been targeted against the removal of most of the ethical topics from the Japanese version of the film, such as part of Mewtwo's origin story. Despite divided reviews (including Japan and the United States), it was a box office success worldwide, topping the box office charts in its opening weekend and eventually grossing over $172 million at the worldwide box office. It also sold 10 million home video units in the United States, including 4.2 million VHS sales that earned $58.8 million in 2000.

During the end credits of Pokémon the Movie: The Power of Us (2018), it was announced that a full CGI remake was set to release the following year. It was released as Pokémon: Mewtwo Strikes Back – Evolution in July 2019.