Obesity is becoming an escalating global epidemic in many parts of the world and results in a huge rise of sanity costs due to its associate comorbidities. In this sense, body weight regulation depends on a combination of interactions between genetic and environmental factors. Among inheritance factors, body weight is normally a polygenic condition determined by the presence of genes of high prevalence but with a low relevant effect. In the last years, Candidate Genes Analyses and Genome Wide Association Studies (GWAS) have become very useful strategies to detect new polymorphisms and copy number variants (CNVs) associated with obesity and its related comorbidities. From these studies, more than a hundred genetic variants involved in metabolic pathways including adipogenesis, energy intake, lipolysis or energy expenditure have been found. These findings along with epigenetics and nutrigenetics are the basis to the development of new tools that would allow predicting individual obesity susceptibility and weight loss response.