The frequency of venous thromboembolism (VTE) is rising in patients with cancer. VTE contributes to mortality and morbidity, but the risk for VTE can vary widely between individual patients. Clinical risk factors for VTE in cancer include primary site of cancer, use of systemic therapy, surgery, and hospitalization. Biomarkers predictive of VTE include platelet and leukocyte counts, hemoglobin, D-dimer, and tissue factor. A recently validated risk model incorporates 5 easily available variables and can be used clinically to identify patients at increased risk of VTE. In high-risk settings, including surgery and hospitalization, thromboprophylaxis with either unfractionated heparin or low-molecular-weight heparins has been shown to be safe and effective. Recent studies have also suggested a potential benefit for thromboprophylaxis in the ambulatory setting, although criteria for selecting patients for prophylaxis are not currently well defined. This article focuses on recent and ongoing studies of risk assessment and prophylaxis in patients with cancer.