Summer Wars (Japanese: サマーウォーズ, Hepburn: Samā Wōzu) is a 2009 Japanese animated science fiction film directed by Mamoru Hosoda, produced by Madhouse, and distributed by Warner Bros. Pictures. The film's voice cast includes Ryunosuke Kamiki, Nanami Sakuraba, Mitsuki Tanimura, Sumiko Fuji, and Ayumu Saitō. The film tells the story of Kenji Koiso, a timid eleventh-grade math genius who is taken to Ueda by twelfth-grade student, Natsuki Shinohara to celebrate her great-grandmother's 90th birthday. However, he is falsely implicated in the hacking of a virtual world by a self-aware, sadistic artificial intelligence named Love Machine. Kenji must repair the damage done, and find a way to stop the rogue computer program from causing any further chaos.

After producing The Girl Who Leapt Through Time, Madhouse was asked to produce something new. Hosoda and writer Satoko Okudera created a story about a social network and a stranger's connection with strange family. The real-life city of Ueda was chosen as the setting for Summer Wars as part of the territory was once governed by the Sanada clan and was close to Hosoda's birthplace in Toyama. Hosoda used the clan as the basis for the Jinnouchi family after visiting his then-fiancée's home in Ueda.

Production of Summer Wars commenced in 2006. Art director Youji Takeshige incorporated Japanese houses into his background designs. Hosoda also insisted that 80 family members were to be included as main characters. The project was first announced at the 2008 Tokyo International Anime Fair and the first trailer of the film was released in April 2009. Audience interest was fueled primarily through word of mouth and Internet publicity. A manga adaptation of the film was written by Iqura Sugimoto and began its serialization in July 2009.

Summer Wars premiered in Japan on August 1, 2009. It grossed over US$1 million in its opening weekend in 127 theaters and ranked No. 7 at the box office. The film was well-received by critics and the general audience and was financially successful, earning $18 million worldwide. It won several awards such as the 2010 Japan Academy Prize for Animation of the Year, the 2010 Japan Media Arts Festival's Animation Division Grand Prize, the Anaheim International Film Festival's Audience Award for Best Animated Feature and was nominated for the 2009 Golden Leopard award at the Locarno International Film Festival.