Understanding the relationship between energy balance and obesity is essential to develop effective prevention programs and policies. The International Agency for Research on Cancer convened a Working Group of world-leading experts in December 2015 to review the evidence regarding energy balance and obesity, with a focus on low- and middle-income countries, and to consider the following scientific questions: (i) Are the drivers of the obesity epidemic related only to energy excess and/or do specific foods or nutrients play a major role in this epidemic? (ii) What are the factors that modulate these associations? (iii) Which types of data and/or studies will further improve our understanding? This book provides summaries of the evidence from the literature as well as the Working Group's conclusions and recommendations to tackle the global epidemic of obesity.