Knowledge of the development and evolution of the neural crest sheds light on many of the oldest unanswered questions in developmental biology. What is the role of germ layers in early embryogenesis? How does the nervous system develop? How does the vertebrate head arise developmentally and how did it arise evolutionarily? How do growth factors and Hox genes direct cell differenti ation and embryonic patterning? What goes wrong when development is misdi rected by mutations or by exposure of embryos to exogenous agents such as drugs, alcohol, or excess vitamin A? In 1988, I was instrumental in organizing the publication of a facsimile reprint of the classic monograph by Sven Horstadius, The Neural Crest: Its properties and derivatives in the light of experimental research, which was originally pub lished in 1950. Included with the reprint was my analysis of more recent studies of the neural crest and its derivatives. The explosion of interest in and knowledge of the neural crest over the past decade, however, has prompted me to produce this new treatment. Here, as in my 1988 overview, I take a broad approach to the neural crest, dealing with its discovery, its embryological and evolutionary ori gins, its cellular derivatives-in both agnathan and jawed vertebrates or gnathos tomes-and the broad topics of migration and differentiation in normal development. Cells from the neural crest are also associated with many develop mental abnormalities.