This book explores the profound importance of phenotypic plasticity as a central organizing theme for understanding biology. Chapters take a broad integrative approach to explain how physical and biological environmental stimuli (temperature photoperiod nutrition population density predator presence etc.) influence insect biochemical physiological learning and developmental processes altering phenotype which then influences performance ecology life-history survival fitness and subsequent evolution. Topics include endocrinology development body size allometry polyphenism reproduction reproductive and life-history tradeoffs alternative mating and life-history strategies density-dependent prophylaxis physiological adaptation acclimation homeostasis heat-shock proteins learning adaptive anti-predator behavior and evolution of phenotypic plasticity.