Anabolic Androgenic Steroids (AASs) are chemical and pharmacological derivatives of the male hormone testosterone which are widely used for increasing burst and sprinting activities in sports. Although AASs are thought to be transversal to the plurality of sports disciplines, they are principally misused by bodybuilders, weightlifters, shot, hammer, discus or javelin throwers, rugby and American football players as well as by swimmers and runners. AAS exert a kaleidoscope of effects on human biology, principally through the 5-α-reductase-mediated conversion into dihydrotestosterone, the aromatase-mediated conversion into female sex hormones, a competitive antagonism to the glucocorticoid receptors, the potential stimulation of erythropoietin secretion as well as psychoactive effects on the brain. The influence of AASs on physical performance is still undefined, since the large number of studies published so far have described discordant and often contradictory outcomes. Nevertheless, animal and human investigations support the hypothesis that the administration of AASs might increase lean body mass, muscle mass, and maximal voluntary strength especially in men, so that they would represent an appealing form of doping for increasing power capacity, sustaining intensive training periods and, last but not least, as a cosmetic muscle makeover. The aim of this article is to review the biochemistry, physiology and the ergogenic effects of AASs.