The invention provides Chlamydia antigens for use in the treatment, prevention and/or diagnosis of Chlamydia infection. In particular, the invention provides antigens CT733, CT1 53, CT601, CT279, CT443, CT372, CT456, CT381, CT255, CT341, CT716, CT745, CT387, CT812, CT869, CT166, CT175, CT163, CT214, CT721, CT127, CT043, CT823 and/or CT600 from C. trachomatis for the treatment, prevention or diagnosis of Chlamydia infection.