he hedgehog signalling pathway is highly conserved and seen in organisms ranging from Drosophila to humans. This pathway is Tcritical in determining cell fate decisions in a variety of different cell types. There are several vertebrate analogues of the Drosophila hedgehog protein of which the most widely studied is Sonic hedgehog (Shh). Shh signalling classically involves the Gli family of zinc-fmger transcription factors. The Shh signalling pathway is well characterised in the develop­ ment of a number of vertebrate organ systems. It could indeed be argued that the Shh and Gli signalling may well be involved at some stage in the development of all the major organ systems in vertebrates. This volume rep­ resents a concerted drive to bring together *state of the art' reviews by lead­ ing experts in the field of Shh and Gli signalling in development from all over the world. The chapters span vertebrate organisms from zebrafish to humans and cover development of the multiple organ systems in which the Shh signalling pathway is crucial for normal development. There are chap­ ters on the development of the central nervous system, skeletal struc­ tures, visceral organs, prostate, lung, immune system and the structures of the human face. The authors themselves span three major continents and multiple nationalities which admirably illustrates the worldwide nature of the science.