The metabolic syndrome (MSynd) refers to a clustering of cardiovascular risk factors characterized by obesity, impaired glucose tolerance/type 2 diabetes, atherogenic dyslipidemia, and hypertension. The tendency that multiple risk factors were often present in the same individual prompted researchers to search for the underlying pathophysiology of the MSynd. In an inventory of hypotheses on causative mechanisms for the MSynd, plausible mechanisms include insulin resistance, leptin resistance, visceral obesity, beta-cell dysfunction, endothelial dysfunction, neuroendocrine origin (sympathetic overactivity and vagal impairment, reduced serotonergic responsivity, endocannabinoid system overactivity), genetic predisposition and fetal origin. The etiology of the syndrome is complex and each hypothesis may explain part of the etiological cascade. More studies are needed to elucidate relevance of and relationship between diverse hypotheses.