We are interested in understanding the mechanisms that normally generate complex structures in the developing mammalian embryo. In particular, we have adopted the mammalian kidney, neural tube and limb skeleton as complex systems for analysis. In these models we have identified a number of critical signals, including members of the Wnt and Hedgehog pathways, that regulate the normal development of these structures. Our expectation is that a firm understanding of the normal regulatory principles that build organ systems will enable an informed and logical approach towards the long-term goal of regenerative medicine; an approach with enormous potential for the treatment of human disease.