Obesity is a disease state that has reached epidemic proportions, with increasing prevalence and serious health care consequences; therefore, it is important to diagnose and evaluate it properly. In this first part of the chapter, we present criteria for the diagnosis of overweight and obesity and evaluation of the obese and overweight patient and emphasize the importance of determining the specific type of obesity and the possible presence of other risk factors in obese individuals. We also review obesity-screening recommendations and rationale. These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.