Biodiesel is an alkyl ester of long chain fatty acids and is considered to leave smaller footprint on the environment. It is produced by transesterification of a fat/oil with a short chain primary alcohol like methanol or ethanol. The three routes to its preparation are: alkali catalyzed, acid catalyzed and lipase-catalyzed transesterification. This review summarizes the key patents filed over the last few decades. The chemistry used in these patents is one of the three routes mentioned above. In few patents, heterogeneous catalysts have been used for catalyzing the transesterification process. The innovations mostly concern fine-tuning of the reaction conditions, plant design to improve logistics and use of glycerol produced as a by-product during biodiesel production. There is a concern that biofuels like biodiesel cut into resources like land meant for food crop production. Life cycle studies also create doubt about there being energy efficient fuels. Judicious choices that would differ with different regions are recommended. For the next few decades till better alternatives like hydrogen become viable, biodiesel would continue to be an important "alternative fuel".