Acute colonic diverticulitis is a gastrointestinal condition that is frequently encountered by primary care and emergency department practitioners, hospitalists, surgeons, and gastroenterologists. Clinical presentation ranges from mild abdominal pain to peritonitis with sepsis. It is often diagnosed on the basis of clinical features alone, but imaging is necessary in more severe presentations to rule out such complications as abscess and perforation. Treatment depends on the severity of the presentation, the presence of complications, and underlying comorbid conditions. Medical and surgical treatment algorithms are evolving. This article provides an evidence-based, clinically relevant overview of the epidemiology, diagnosis, and treatment of acute diverticulitis.