CD97, a membrane protein expressed at high levels on inflammatory cells and some carcinomas, is a member of the adhesion G protein–coupled receptor family, whose members have bipartite structures consisting of an extracellular peptide containing adhesion motifs noncovalently coupled to a class B 7-transmembrane domain. CD97α, the extracellular domain of CD97, contains 3 to 5 fibrillin class 1 epidermal growth factor (EGF)–like repeats, an Arg-Gly-Asp (RGD) tripeptide, and a mucin stalk. We show here that CD97α promotes angiogenesis in vivo as demonstrated with purified protein in a directed in vivo angiogenesis assay (DIVAA) and by enhanced vascularization of developing tumors expressing CD97. These data suggest that CD97 can contribute to angiogenesis associated with inflammation and tumor progression. Strong integrin α5β1 interactions with CD97 have been identified, but αvβ3 also contributes to cell attachment. Furthermore, soluble CD97 acts as a potent chemoattractant for migration and invasion of human umbilical vein endothelial cells (HUVECs), and this function is integrin dependent. CD97 EGF-like repeat 4 is known to bind chondroitin sulfate. It was found that coengagement of α5β1 and chondroitotin sulfate proteoglycan by CD97 synergistically initiates endothelial cell invasion. Integrin α5β1 is the first high-affinity cellular counterreceptor that has been identified for a member within this family of adhesion receptors.