Beginning with the description of the term "obesity" and its history, this chapter first reviews the different measures of obesity for epidemiological as well as clinical studies. All practically used measures of obesity are argued to be proxy measures of body fatness, and the excess fatness is the consequence of energy imbalance or disregulation of energy homeostasis. Health consequences and disease association of obesity is reviewed suggesting that central body fatness is the major obesity-related risk factor for untoward health outcome. Causes of obesity is the next subject reviewed, indicating that obesity is truly an "unhappy" multifactorial phenotype, having influences of inherent individual genetic make-up as well as those of environmental and lifestyle insults. The nature of these multifactorial etiological factors is the thrust of this reviewed topic. Current activities toward combating the worldwide obesity epidemic are mentioned, with examples of multifaceted strategies and plans involving individual as well as societal involvement in such efforts. The chapter ends with some suggestions for further research on bioinformatics of obesity that may have translational value in enhancing the efficacies of modalities of prevention and control of obesity.