Endoscopy can be used to identify the exact cause and iste of acute upper gastrointestinal bleeding in over 95% of cases. Findings at urgent endoscopy can contribute to precise prediction of rebleeding, guide triage of patients, and in most cases lead to definitive endoscopic therapy or direct surgical management. Making an accurate diagnosis during urgent endoscopy can be challenging; analogous to endoscopic retrograde cholangiopancreatography (ERCP), where cannulation of the desired duct is the major initial hurdle to performing therapy, in gastrointestinal (GI) bleeding, the prerequisite to endoscopic hemostasis is clear identification and access to the bleeding site. Thorough knowledge of the differential diagnosis and natural history of various causes of acute upper GI bleeding is essential. Emergency endoscopy in the acute GI bleeder can be technically difficult and risky to the patient and can require close coordination with intensive care physicians and nurses. Cardiopulmonary complications causing severe morbidity, such as aspiration of blood, usually can be avoided by careful attention to details of resuscitation and medical management, before, during, and after endoscopy.