A growing body of evidence implicates Wnt signaling in the control of angiogenesis. To better understand the role of the Wnt/β-catenin pathway in endothelial cells (EC), we examined endogenous signaling activity and signaling component expression in vascular cells. We observed stabilization of cytosolic β-catenin and activation of a T-cell factor (TCF) -luciferase promoter, hallmarks of canonical Wnt signaling activity, in cultured EC. This activity was increased in subconfluent EC, which are known to display characteristics of angiogenic EC, compared with confluent EC, which have a more differentiated phenotype. Endogenous TCF activity was inhibited by transfection with a secreted inhibitor of canonical Wnt signaling. A systematic analysis of Wnt, Fzd, SFRP, and Dkk gene expression in human EC (cultured and freshly isolated), smooth muscle cells (cultured), and aorta demonstrated that numerous Wnt signaling components are expressed by vascular cells. We conclude that Wnt signaling components are expressed and active in cultured EC. Developmental Dynamics 235:3110–3120, 2006. © 2006 Wiley-Liss, Inc.