Infections of the gastrointestinal tract can often involve the gallbladder. Infection probably plays a role in the formation of gallstones but is more commonly thought to contribute to acute illness in patients. Acute calculous cholecystitis caused by an impacted gallstone is often complicated by secondary bacterial infection and is a major cause of morbidity and even mortality in patients. A wide variety of organisms can be associated with acute acalculous cholecystitis, a less common but potentially more severe form of acute cholecystitis. This review focuses on infections and their role in the above-mentioned processes involving the gallbladder.