The role of body weight on human reproductive function and fertility has received considerable attention in the medical literature. Time-to-pregnancy studies are very useful in determining the overall effects of any exposure on overall fertility. Studying the role of overweight and obesity among couples undergoing assisted reproductive technology (ART) can serve multiple purposes. First, it provides clinically useful information addressing the specific needs of infertile couples. Second, ART provides a unique opportunity to study the role of obesity on reproductive physiology and pathology. Obesity leads to a wide range of systemic alterations including changes in circulating levels of adipokines, reproductive hormones, markers of endothelial dysfunction, and systemic inflammation, as well as metabolic disturbances in lipoprotein metabolism, glycemic control, and increased insulin resistance. The existing evidence on whether clinical management of obesity has any effects on fertility is mostly limited to women with polycystic ovary syndrome (PCOS).