Developmental biology deals with the regulatory principles underlying the generation of a new organism. The up-to-date knowledge of the molecular and cellular mechanisms that guide mammalian development from a single cell through a complex and integrated process of cell multiplication, differentiation and organisation of cells into tissues and organs is presented in this volume. Aspects of the molecular nature and developmental significance of cell-to-cell signals focus on: - hoxgenes, their products and potential role in mammalian morphogenesis; - growth factors, their receptors and signal transduction, and their role in guiding cell multiplication, differentiation and transformation; and - cell adhesion and extracellular matrix molecules, as short-range cell-to-cell signals in mammalian development.