Kingdom Hearts 358/2 Days (subtitle read as "Three-Five-Eight Days over Two") is an action role-playing video game developed by h.a.n.d. and Square Enix in collaboration with Disney Interactive Studios for the Nintendo DS. It is the fifth installment in the Kingdom Hearts series, and takes place near the end of the first game in parallel to Kingdom Hearts: Chain of Memories, leading directly into the events of Kingdom Hearts II. The game was released worldwide in 2009. The story is told from the perspective of Roxas, and follows his daily life within Organization XIII and his relationship with fellow Organization member Axel; it also introduces a fourteenth member, Xion, who befriends them.

Kingdom Hearts 358/2 Days was directed by Tetsuya Nomura and Tomohiro Hasegawa. Nomura decided to develop a game for the Nintendo DS, and once a system had been chosen, decided upon Roxas as the protagonist. The development team wanted to use gameplay similar to previous Kingdom Hearts games, but could not due to the DS's insufficient number of buttons. Kingdom Hearts 358/2 Days received generally positive reception, with praise for the gameplay and graphics but criticism for its storyline and controls. A soundtrack, various light novels, and a manga series based on the game were released in Japan.

The game was dedicated to Wayne Allwine, the longtime English voice of Mickey Mouse, who died on May 18, 2009, 12 days before the game's release in Japan. 358/2 Days was the final game to feature his performance as Mickey, though his performance was archived and reused in remastered ports of older games released after his death.