The Chlamydiaceae are a family of gram-negative bacteria that belongs to the phylum Chlamydiota, order Chlamydiales.

Chlamydiaceae ribosomal RNA genes all have at least 90% DNA sequence identity.

C. trachomatis has been found only in humans, C. muridarum in hamsters and mice (family Muridae), and C. suis in swine.

Chlamydia species produce a small amount of detectable glycogen and have two ribosomal operons.

Chlamydia trachomatis is the cause of an infection commonly transmitted sexually (often referred as just "Chlamydia") and also is the cause of trachoma, an infectious eye disease, spread by eye, nose, and throat secretions.