Leading international experts contribute to this selection of reviews covering the merging fields of growth factors, differentiation factors, and cytokines. These appear to play fundamental roles in a wide variety of physiological and pathophysiological processes that include the regulation of growth in normal and malignant cells, embryogenesis, the immune response, wound healing, inflammation, and atherogenesis. The major aspects of recent research and development are discussed, providing an important update in this pioneering field.