Angiogenesis is essential for the development and growth of tumors. It is a highly regulated process that requires cross-talk between signaling pathways at all stages of blood vessel development and tumor growth, from the recruitment of endothelial cells to vessel maturation. This review summarizes tumor angiogenesis and describes the key signaling pathways governing blood vessel development. The role of angiogenesis in various tumor types is discussed, but the focus is on invasive breast cancer, a disease that will affect approximately 182,000 women in the USA in 2008. Research efforts over the past decade have identified numerous potential, as well as proven therapies with activity in breast cancer. These include chemotherapeutics as well as therapies that inhibit specific angiogenic pathways known as targeted agents. Some of the data from single- and multitargeted antiangiogenic agents are described in this review. "Published 2008 Wiley-Liss, Inc. This article is a US Government work, and, as such, is in the public domain in the United States of America."