Evaluation of the emergency department patient with acute abdominal pain may be challenging. Many factors can obscure the clinical findings leading to incorrect diagnosis and subsequent adverse outcomes. Clinicians must consider multiple diagnoses with limited time and information, giving priority to life-threatening conditions that require expeditious management to avoid morbidity and mortality. This article seeks to provide the clinician with the clinical tools to achieve these goals by reviewing the anatomic and physiological basis of abdominal pain and key components of the history and the physical examination. In addition, this article discusses the approach to unstable patients with abdominal pain.