Circadian rhythms are such an innate part of our lives that we rarely pause to speculate why they even exist. Some studies have suggested that the disruption of the circadian system may be causal for obesity and manifestations of Metabolic Syndrome (MetS). Shift-work, sleep-deprivation and bright-light-exposure at night are related to increased adiposity (obesity) and prevalence of MetS. It has been provided evidence of clock genes expression in human adipose tissue and demonstrated its association with different components of the MetS. Moreover, current studies are illustrating the particular role of different clock genes variants and their predicted haplotypes in MetS. The purpose of “Chronobiology and Obesity� is to describe the mechanisms implicated in the interaction between chonodisruption and metabolic-related illnesses, such as obesity and MetS, with different approaches.