Angiogenesis—one of the hallmarks of cancer—has emerged as a valid therapeutic target in oncology. The VEGF system represents a key mediator of tumor-initiated angiogenesis and the first target of antiangiogenesis agents introduced in clinical practice. Although anti-VEGF therapies have clearly demonstrated antitumor efficacy in various malignancies, especially when combined with conventional cytotoxic chemotherapy, their mechanism of action is not fully understood. This Review will discuss the rationale for using antiangiogenic compounds and will focus on large molecules, such as antibodies, that target the VEGF system. Clinical data on bevacizumab is discussed in detail. Predictive markers for anti-VEGF agents have not yet been identified and questions regarding the usefulness of bevacizumab in the adjuvant setting as well as its continued use beyond progression remain unanswered, in spite of negative data on bevacizumab in treating patients with adjuvant colon cancer. Nonetheless, anti-VEGF therapy has enhanced the arsenal of anticancer therapies and has provided new insights into the biology of malignancy.