Diarrhea generates a wide range of diagnostic considerations and has profound individual and public health significance. The setting and circumstances under which a patient presents with diarrhea drastically influences the concern brought to the encounter. Nausea, vomiting, and diarrhea are often provisionally labeled “gastroenteritis” with appropriate expectant management. In resource-poor countries, the significance of diarrhea is even greater. This review focuses on diarrhea and its initial evaluation and management in the emergency department.