Abstract: Ecological energetics involves the application of energetics to address questions of interest to population biologists.These questions cover a variety of topics,ranged from the adaptive significance of sex,life history evolution,behavioral allocation and trade-off to reproductive and mating systems or foraging str ategies.This review has following parts:principles of evolutionary optimization,the relationship between energy expenditure and fitness,the approaches of de scribing life history,how could energy budget be regularized by supply or demand,the links of energy with structure and function,energy and foraging theory, and energy allocation and sexual selection.