The present paper reviews the metabolic basis of different methods for fermentative glycerol production. The most important microbial production organism is the yeast Saccharomyces cerevisiae but other yeast species, as well as molds, algae, and bacteria are of potential interest for glycerol production. A large variety of methods have been applied to increase the fermentative glycerol yield. The first methods were based on physiological control, e.g. chemically induced overproduction of glycerol through NADH entrapment by the addition of chemical steering agents (such as bisulfite). More recently, genetic engineering of the glycolytic pathway has been used to improve production, involving modulated function of e.g. triose phosphate isomerase, phosphoglycerate mutase, PDC or alcohol dehydrogenase. Direct intervention in the glycerol pathway, such as overexpression of G3P dehydrogenase, has also been tried. The applied strategies can be divided into three principal groups; (a) deactivation or down-regulation of NADH oxidation sites alternative to G3P dehydrogenase, (b) increase of NADH generation or, (c) direct changes in the carbon flux to glycerol.