The development of tissues and organs in multicellular organisms is controlled by the interplay of several signaling pathways that cross-talk to provide positional information and induce cell fate specification. Together with other families of secreted factors such as TGFßs, FGFs, Hedgehog and Notch proteins, Wnt growth factors are crucially implicated in these processes. Here, we will first discuss molecular mechanisms and then consider some biological consequences of Wnt signaling