Despite the fact that venous thromboembolism (VTE) is one of the most widely studied areas in medicine, and despite the availability of data from numerous RCTs, there are many areas where the evidence is insufficient to allow grade A recommendations to be made. In these areas published guidelines often differ in their advice. In this chapter we primarily discuss the National Institute of Clinical and Health Excellence (NICE) VTE prophylaxis pathways in the context of other guidance published by the Scottish Intercollegiate Guideline Network and the American Colleges of Physicians and Chest Physicians. Evidence for the use of both mechanical and pharmacological thromboprophylaxis is discussed for both medical and surgical patients.