Studies of the cells and genes of the nematode C. elegans have become a cornerstone of current biology. A classic 1988 Cold Spring Harbor monograph described the basic genetics, anatomy and development of the organism. Now, in that authoritative tradition, comes C. elegans II -- not a second edition but a book that breaks new ground and defines the current status of the field, providing a detailed molecular explanation of how development is regulated and the nervous system specifies varied aspects of behavior. This volume is a must for any investigator doing worm studies but it has been written and rigorously edited to illuminate for a wider community of investigators in cell and molecular biology who should know how new knowledge of C. elegans relates to their own specialty.