The physiological challenges initiated by food limitation and the risk of death by starvation were likely faced by the very first animals and show no signs of abatement within the foreseeable future. Comparative physiologists are charged with identifying and characterizing the mechanisms by which different animals persist, and even thrive, despite the often present threat of food scarcity. Over the past century only a handful of books have focused on the physiological effects of starvation and none considered this phenomenon from a broadly comparative perspective. Exploring the physiology of starvation from a comparative point of view is not simply an academic exercise. In fact, knowledge from comparative investigations routinely leads to practical applications, from the development of novel investigative techniques and the identification of new model organisms, which can lead to medical advances, to improving conditions for economically important animals, reducing damage by pest species, and to developing accurate predictions about how impending climate change will impact biological systems at various levels. Historically, physiologists have studied fasting and starvation in their respective animal models with minimal intercourse in the literature and too little serious exchange of ideas. It is now clear that progress in understanding fasting and starvation physiology will be most rapid through the use of integrative and comparative approaches, which will require synthesis of the existing encyclopedic body of facts and data into a robust conceptual framework from which new ideas and theories will extend. The chapters in this volume highlight the tremendous progress we have made in developing new tools and skills to study fasting and starvation. These tools range from remote sensing using global positioning systems, to DNA microarray analysis; whole-body MRI to isotope analyses of individual hairs; and analytical chemistry to population modeling. Despite the technological revolution that has occurred, future progress will continue to require input from our colleagues in the field who have detailed knowledge of the natural histories of various species. Chapters were contributed by researchers currently investigating fasting and starvation physiology using animal models that span from invertebrates to humans.