Acute appendicitis is a common pediatric abdominal emergency, although it can occur in any age group. The debated role of imaging in diagnosis and diagnostic delays make diagnosis particularly challenging in the elderly. Given the heterogeneity of the population that may be affected by this disease, it is not possible to stipulate a universally valid diagnostic process. As such, an individualized approach guided by age, sex, comorbidities, and clinical manifestations is always necessary. This book reviews the current state of the art in acute appendicitis to help surgeons administer proper and timely treatment.