This volume is devoted to the 21 rattlesnakes belonging to the genus Crotalus of the family Viperidae.  Each species has its own account, which includes a detailed description, geographic variation and confusing species, karyotype and fossil record (if known), distribution, and habitat preferences. These are followed by a detailed life history, a description of its venom delivery system, and discussions of its venom and envenomation symptoms and severity. Literature cited is through June 30, 2010.  The species accounts are followed by a glossary of scientific names, a bibliography, and an index to common and scientific names. 