The Notch signaling pathway is conserved in vertebrates and invertebrates and is involved in many developmental processes. Notch receptors and ligands are expressed on the cell surface enabling interactions between adjacent cells upon receptor–ligand binding. Notch signaling molecules have an important well-documented role in vascular development, differentiation, proliferation, apoptosis and tumorigenesis. Recently, several groups have identified the importance of Notch signaling in tumor angiogenesis. Notch activity increases specifically in tumor endothelium and in various tumors types and, in some studies, Notch signaling suppresses angiogenic processes. Because the Notch signaling pathway can mediate communication between various cell types in the tumor microenvironment, interactions between tumor cells and endothelial cells might promote angiogenesis, therefore targeting the Notch pathway might provide a novel strategy for anti-angiogenic therapies. Here, we discuss recent insights of Notch signaling in tumor angiogenesis.