Venous thromboembolism (VTE) is diagnosed in 1.43 per 1,000 persons each year. It includes pulmonary embolism (PE) and deep vein thrombosis (DVT), most often of the lower extremities, although it may also occur in upper extremities and atypical sites (mesenteric, ovarian, and cerebral veins). Depending on the anatomic location, there are important differences in epidemiology, diagnosis, and treatment of VTE. This chapter explores DVT of lower extremities, upper extremities, and PE as distinct entities.