The biodiesel was the best alternative of petroleum diesel. The 1st generation feedstock would create the food shortage. The second-generation yield was comparatively less and from third generation feedstock the process was complicated and expensive. The fourth-generation feedstock produced from genetically modified algae or by artificial photosynthesis in plants to produce the raw material for biodiesel production The fourth generation was not available on commercial scale. The biodiesel produced by esterification (one step) and Transesterification process (two step). The catalysts used were homogenous, heterogenous and enzymatic. The homogenous were alkaline and acidic. The alkaline catalyst undergoes saponification reaction when free fatty acid concentration was high. The acidic catalyst preparation was expensive and complicate exhibited slow rate of reaction. The biodiesel used in blend form and diesel engines required the modification. The biodiesel sustainable and release no greenhouse gas.