Kingdom Hearts Timeline

The series is mostly in sequential order. The first game in the timeline is Birth by Sleep, telling the story of three keybearers during the Keyblade War. 10 years later is where the first Kingdom Hearts picks up, revolving around the first adventure of Sora. Next is Chain of Memories, taking place in between Kingdom Hearts and Kingdom Hearts II. It also takes place during parts of 358/2 Days. Kingdom Hearts II follows Chain of Memories, and takes place one year after Kingdom Hearts though it is more so a sequel to Kingdom Hearts rather than the Gameboy Advance game. Finally, there is Coded, which takes place right where Kingdom Hearts II left off.

358/2 Days doesn't have a real spot in the timeline, for it takes place from the time Sora turned into a Heartless, to right before the beginning of Kingdom Hearts II, which is 358 days. The 7 days of Kingdom Hearts 2's prequel can be an extension to the DS game. So from when Sora sacrifices himself to when he wakes up is a little more than a year, if you still count the time between the events of Hollow Bastion and the ending of Kingdom Hearts. 358 is also a sequel to Chain of Memories, since the GBA game mentioned "the other side of Sora's heart," and it takes place right after Riku's story, telling what happened from when Riku joined DiZ to his disappearance and search for Roxas.

This is the order of the games released in chronological order within the series:

Kingdom Hearts: Birth by Sleep (PSP)
Kingdom Hearts (PS2)
Kingdom Hearts: Chain of Memories (GBA)
Kingdom Hearts 358/2 Days (NDS)
Kingdom Hearts II (PS2)
Kingdom Hearts coded (Mobile Phones)