OK is the ninth studio album by Taiwanese singer-songwriter Chang Chen-yue. It was released in 2007. The album marked a significant stylistic departure from Chang's previous alternative, electronic, and hard rock style into a more straightforward and melodic pop sound.
The song "Missing is a Type of an Illness" is a cover of Chyi Chin's 1989 song of the same name. Chang additionally incorporated rap into the verses in his rendition and recruited singer Tanya Chua to duet together on the chorus.
Meanwhile, the title track "OK" was written to express Chang's feelings after his breakup with his partner ().