Crude glycerol is the primary by-product of the biodiesel industry and too costly to purify it into a higher quality product. However, glycerol can be converted into other useful products used in the pharmaceutical and cosmetics industries such as trimethylene glycol (1,3-propanediol), propylene glycol (1,2-propanediol), ethylene glycol and ethanol through the hydrogenation process and the microbial fermentation process. This article reviews factors affecting glycerol conversion, glycol selectivity, concentration and conversion yield through both the hydrogenation and microbial fermentation processes.