Somites are blocks of embryonic mesoderm tissue that give rise to skeletal muscle, cartilage, and other connective tissues. The development of different tissues within the somite is influenced by adjacent structures, in particular, the neural tube and notochord. Results of experiments performed in vivo and in vitro suggest that somites contain populations of cells stably programmed to undergo either skeletal myogenesis or chondrogenesis and a population uncommitted to either pathway. The fate of the uncommitted cells would depend on a transfer of information from the committed cells. Communication between committed and uncommitted cells is regulated by cell and tissue interactions that either activate or inhibit this process.