Together with the fibroblast growth factor (FGF), transforming growth factor (TGF)-β, and Hedgehog pathways, the Wnt pathway is one of the four major signaling pathways that are involved in almost every aspect of embryogenesis. Using the mouse as a model organism, research over the last decade has revealed numerous roles of the Wnt pathway in mammalian development. In this chapter, we focus on some of the recent advances in our understanding of how Wnt signaling, through collaboration with other pathways, regulates gastrulation and organogenesis, including neural patterning, heart development, hematopoiesis, and the formation of liver, limb, skin, kidney, lung, and gastrointestinal tract. We also discuss the important function of the novel noncanonical Wnt pathway in polarity establishment and morphogenesis, a process through which a tissue or embryo acquires its final shape. Interestingly, the canonical and noncanonical Wnt pathways share a number of critical components, raising the possibility that patterning and morphogenesis may be intimately linked. © 2007 Elsevier Inc. All rights reserved.