This volume, the proceedings of the Seventh International Conference on Coelenterate Biology, is organized as the meeting was around six topics. Because several sessions of ICCB7 constituted the 2003 North American meeting of the International Society for Reef Studies, the subject of coral reefs is strongly represented in the section on Ecology. The other themes are Neurobiology; Reproduction, Development, and Life Cycles; Pioneers in Coelenterate Biology; Cnidae; and Taxonomy and Systematics. Ctenophores, as well as representatives of all four classes of cnidarians are among the study subjects of the research reported in this volume. The theme of variability runs through the volume – be it in cnidae, morphology, behavior, neurobiology, ecology, colony form, or reproduction, variability is a major reason these animals are so interesting and challenging to study! This is a must-read resource for anyone doing research – or planning to do research – on cnidarians and ctenophores.