This issue of Emergency Medicine Clinics focuses on Observation Medicine in the ED. Editors R. Gentry Wilkseron and Christopher Baugh have assembled an expert team of authors on topics such as: History and Principles of Observation Medicine; Observation Unit Design and Establishing an Observation Unit; Care of the Patient with Chest Pain in an Observation Unit; Care of Cardiovascular Conditions in an Observation Unit; Care of Gastrointestinal Conditions in an Observation Unit; Care of Metabolic / Endocrine Conditions in an Observation Unit; Care of Neurologic Conditions in an Observation Unit; Care of Respiratory Conditions in an Observation Unit; Care of Infectious Conditions in an Observation Unit; Care of Traumatic Conditions in an Observation Unit; Care of Extremes of Age in an Observation Unit.