Obesity is a major risk factor for the development of type 2 diabetes and its associated complications, a major socio-economic burden for health care systems. The worldwide prevalence of obesity doubled since 1980 and as a consequence the number of patients with diabetes has been continuously rising with more than 450 Mio. people suffering from this disease at the present time. Substantial progress has been made in understanding the molecular pathways leading from excessive fat accumulation to metabolic perturbation and finally diabetes manifestation. This edition of the “Handbook of Experimental Pharmacology” aims to analyze new insight into the pathophysiology of obesity, to decipher the complex links to diabetes and its complications, and to collect most recent information on new strategies for prevention and treatment of obesity and diabetes.