Chlamydia psittaci and Chlamydia pneumoniae are important causes of community-acquired pneumonias. Less commonly, C. trachomatis may cause pneumonia in adult immunocompromised hosts but more commonly is responsible for pneumonia in neonates. C. psittaci is the cause of psittacosis and is the only chlamydial zoonotic atypical pneumonia. C. pneumoniae is being increasingly recognized as the cause of up to 10% of community-acquired pneumonias. C. pneumoniae pneumonia has a clinical presentation like Mycoplasma pneumoniae pneumonia. C. pneumoniae is also responsible for a variety of other respiratory tract infections, e.g., sinusitis, bronchitis, otitis, pharyngitis and laryngitis. C. pneumoniae, like M. pneumoniae, may result in permanent airway disease, e.g., asthma, following infection. All chlamydia are sensitive to doxycycline. Macrolides are highly active against C. trachomatis, and in spite of in vitro susceptibility, are relatively inactive in vivo against C. psittaci and C. pneumoniae. Fluoroquinolones are also active against chlamydia. Doxycycline remains the preferred antibiotic to treat all chlamydial infections in nonpregnant adults.