Abstract: Metabolisms are fundamental processes of organisms. The recently-proposed Metabolic Theory of Ecology (MTE) seeks to explain ecological patterns and processes in terms of the effects of body size and temperature on the metabolic processes of organisms and using the scaling approach. James Brown and his colleagues extended the MTE to explain large-scale patterns of species diversity, and proposed a potential mechanism for species richness–temperature relationships, which predicted that the number of species increases exponentially with increasing environmental temperature. More quantitatively, they predicted that (1) log-transformed number of species varies linearly with the reciprocal of absolute temperature, and (2) the slope of the relationship ranges between –0.70 and –0.60. The MTE has generated widespread attention and controversy and has been tested by a number of empirical observations, but no agreement has yet been reached. Although several issues need to be resolved, the theory is quite different from conventional regres-sion-based methods because of its biological mechanism-sound approach. Previous empirical tests of the theory may ignore two important assumptions (i.e. unconstrained environments except temperature and equi-librium communities) that are the basis for understanding the MTE. This article reviews the frame-work, pre-dictions, and biological meanings of the MTE and examines previous empirical tests of the theory. We also comment on criticisms raised by previous studies and prospect some aspects for the further study.