The metabolic syndrome (MetS) represents a cluster of metabolic abnormalities that predisposes an individual to a greater risk of developing coronary heart disease and type 2 diabetes. The condition is widespread among adults from developed nations, and progresses in frequency with age. In recent years, several organizations have proposed diagnostic criteria that could be used by clinical practitioners or for research purposes. While the core components of the MetS have generally been sustained among the various proposed definitions, the number of features required for the MetS to be diagnosed and the cut-off points indicating metabolic perturbations have differed quite significantly between organizations. This has led to considerable confusion among clinicians and health professionals. The present review aims to discuss the different definitions of the MetS, focusing on their application in clinical or research settings. A brief overview of the increasing prevalence of the MetS will also be presented.