The limb has long been considered a paradigm for organogenesis because of its simplicity and ease of manipulation. However, it has become increasingly clear that the processes required to produce a perfectly formed limb involve complex molecular interactions across all three axes of limb development. Old models have evolved with acquisition of molecular knowledge, and in more recent times mathematical modeling approaches have been invoked to explain the precise spatio-temporal regulation of gene networks that coordinate limb patterning and outgrowth. This review focuses on recent advances in our understanding of vertebrate limb development, highlighting the signaling interactions required to lay down the pattern on which the processes of differentiation will act to ultimately produce the final limb.