Hemothorax, defined as the accumulation of blood within the pleural space, most commonly results from blunt or penetrating chest trauma. However, spontaneous or iatrogenic causes, particularly following surgical or procedural interventions, may also occur. The initial clinical presentation varies depending on the rate and volume of blood accumulation and includes dyspnea, chest pain, hypoxia, and hemodynamic instability. Radiologic imaging provides important clues regarding the presence of hemothorax; however, thoracentesis to evaluate the pleural fluid-to-blood hematocrit is required for diagnosis. Management options include observation in small, stable cases. Tube thoracostomy is needed for larger or symptomatic hemothoraces, and lastly, surgical intervention is necessary in a subset of patients. Additional therapies, such as pleural lavage, lytic therapy, and transcatheter arterial embolization, can be utilized in specific scenarios. Early recognition and intervention are essential, as delayed or inadequate management may lead to complications such as fibrothorax and trapped lung, with increased mortality. This chapter provides a comprehensive review of hemothorax, including epidemiology, presentation, diagnosis, treatment, and prognosis.