Publisher summary : The expression of phenotypic plasticity is widespread in insects. One of the most extraordinary and economically devastating examples of phenotypic plasticity is found in locusts. In contrast to typical grasshoppers, locust species express an extreme form of density-dependent phenotypic plasticity known as "phase polyphenism." Environmental factors such as temperature, photoperiod, resource availability and population density, are known to affect the development of a myriad of phenotypic traits that have consequences for individual performance, ecology, life-history, fitness and subsequent evolution. Given their diversity of responses and amenability to experimental manipulation and rearing in the lab, insects continue to play an important role as model organisms in empirical analyses of the fundamental relationships between genotypes and phenotypes in animals. Critical conclusions and recommendations from the analysis of recent laboratory stocks, findings that are broadly applicable across taxa to any research program rearing organisms in the lab, are also given in the chapter