Publisher Summary This chapter discusses dormancy, which is an inactive state associated with metabolic depression and arrested development that promotes the survival of insects during periods of harsh environmental conditions, including high or low temperatures or moisture conditions and reduced food quality or availability. Dormancy may be manifested in a variety of forms that differ widely in their intensity and duration. Consequently, it has been proven difficult to classify these forms into discrete categories, and general agreement on terminology is lacking. Quiescence commonly refers to short periods of dormancy that are directly induced by adverse environmental conditions, principally low or high temperature. It also has the advantage of being quickly reversible upon the return of favorable conditions; this rapid response may be especially important in extreme environments, such as alpine regions or deserts, where access to food and favorable conditions are intermittent and unpredictable.