Reviews effects of allocation decisions on life history and demography, and notes biological constraints affecting these allocation decisions. Effects of environmental variation on foraging decisions, and hence on resource input to be allocated, are outlined. Examination of the physiology of allocation focuses on the relationship between rates and efficiencies of growth or reproduction. The author suggests an approach to understanding allocation that is based on physiological and ecological considerations, and concludes with ideas about how this can be used to understand an organism's life strategy. -from Author