Chlamydia is a common sexually transmitted infection (STI) caused by the bacterium Chlamydia trachomatis. It often affects the genitals, rectum, and throat, and many people—especially women—have no symptoms. When present, symptoms can include burning with urination, abnormal discharge, rectal pain, or pelvic/testicular discomfort. If untreated, chlamydia may lead to pelvic inflammatory disease (PID), infertility, or ectopic pregnancy in women, and epididymitis in men. Diagnosis is typically made with a nucleic acid amplification test (NAAT), and treatment involves a short course of antibiotics such as doxycycline. Routine screening, safe sex practices, and treating sexual partners are key to prevention and control.