Thromboprophylaxis is underused in patients with cancer, despite the fact that malignancy is a serious risk factor for venous thromboembolism in this population. Major medical guidelines, including those published recently by the American College of Chest Physicians, the American Society of Clinical Oncology, and the National Comprehensive Cancer Network, recommend routine thromboprophylaxis for patients with cancer under certain situations. This review describes current recommendations for primary and secondary prophylaxis in patients with cancer.