Chlamydia is a sexually transmitted infection caused by the bacterium Chlamydia trachomatis. This bacterium can infect both men and women and can be transmitted through unprotected vaginal, anal, or oral sex with an infected person. Chlamydia is one of the most common sexually transmitted infections and can lead to serious health problems if left untreated. Symptoms of chlamydia can include painful urination, discharge from the genitals, and pelvic pain, although many people with chlamydia do not experience any symptoms. Testing and treatment are available for chlamydia, and it is important to seek medical attention if you think you may have been exposed to the infection.