population level and to provide the methods to study them. It is intended to be a catalyst leading to gender-specific treatments of metabolic diseases. There are fundamental aspects of metabolic homeostasis that are regulated differently in males and females, and influence both the development of diabetes and obesity and the response to pharmacological intervention. Still, most preclinical researchers avoid studying female rodents due to the added complexity of research plans. The consequence is a generation of data that risks being relevant to only half of the population. This is a timely moment to publish a book on sex differences in diseases as NIH leadership has asked scientists to consider sex as a biological variable in preclinical research, to ensure that women get the same benefit of medical research as men.