The technique of allometry investigates the effects of size on such variables as food intake, energy requirements, growth rates, and age at first reproduction. Reiss brings together much of what is known about the consequences of size and provides a new and mathematically rigorous framework within which many quantitative predictions are made and tested using published and unpublished data. The models presented afford a new synthesis of the effects of size and open up pathways for further theoretical investigation and experimental testing. Care has been taken to give verbal presentations of all the mathematical conclusions to ensure that the text is widely intelligible.