Book excerpt: Continuing the tradition set by the first and second editions, each a bestseller in its own right, the third edition of Immunotoxicology and Immunopharmacology provides reviews of environmental agents, updated to reflect the latest information on how these agents influence immune system function and health. For the first time in the book's history, an entire section covers the phylogeny and ontogeny of the immune system, spanning levels of biological complexity from earthworms to marine mammals.