Thrombophilias can be defined as a group of inherited or acquired disorders that increase the risk of developing thrombosis. Venous thromboembolism (VT) is considered a multifactorial disease produced by a sum of risk factors that predispose to the thrombotic event. This predisposition includes genetic and acquired defects. Thrombosis can occur in any section of the venous system, but commonly manifests as deep vein thrombosis of the leg and pulmonary embolism. Major complications of venous thrombosis are a disabling post-thrombotic syndrome, pulmonary hypertension, and sudden death duo to a pulmonary embolism and therefore, it poses a burden on health economy. Venous thrombosis is a common clinical challenge for doctors of all disciplines, as it is a complex multicausal disease. This books discusses in further detail the many complications and risk factors caused by venous thrombosis.