Botanists and zoologists have recognized for centuries the specificity of various insects for plants, and entomolo- gists have long been aware that insects defend themselves from predators by emitting repulsive odors. Only recently have chemists and biologists established a joint endeavor for studying the chemical relationships between plants and insects. The present symposium volume of the Phytochemical Society of North America's RECENT ADVANCES IN PHYTOCHEMISTRY consists of eight papers dealing with phytochemical relation- ships between plants and their insect herbivores. The fifteenth P.S.N.A. annual symposium and meeting was held in August, 1975, on the campus of The University of South Florida, Tampa. The chemical defenses of apparent and unapparent plants were contrasted by Feeny. Rodreguiz and Levin illustrated parallel defense mechanisms of plants and insects and then Hendry, Kostelc, Hindenlang, Wichmann, Fix and Koreniowski discussed chemical messengers for both plants and insects. Subsequently Beck and Reese reviewed plant contributions to insect nutrition and metabolism. Indepth studies for the monarch butterfly-milkweed interaction were presented by Roeske, Seiber, Brower, and Moffitt and for the cotton boll weevil-cotton plant relationship by Hedin, Thompson, and Gueldner. In the latter portion of the symposium Rhoades and Cates presented a general theory concerning the coevolu- tion of insects and plant antiherbivore chemistry.