Wnt genes code for a family of secreted glycoproteins which fulfil important functions during the development of vertebrates and invertebrates. Wnts regulate as different aspects as differentiation, proliferation, cell migration, and cell polarity. Wnt proteins are able to activate different intracellular signaling cascades. This book describes different aspects of Wnt signaling during development of different species like the mouse, Xenopus, chicken, C. elegans or Drosophila and in different cellular contexts like heart formation or limb bud patterning. By doing such, this book provides, for the first time in printed form, an overview of the function of Wnt proteins during development. This book will be of interest to all professionals in the field of Wnt signaling, signal transduction or animal development.