Over the last years citric acid was produced by direct extraction from citrus fruits. By this method the production rate and purification was very low which was unable to meet the increasing demand of the citric acid in the market, also the waste generated during production was very high that lead to environmental concern. There is a demand of alternative method that can produce Citric acid at low cost, high production rate and generate less waste. For this, fermentation techniques were introduced for the production of the citric acid. Citric acid is one of the commercial important organic acid produced by the fermentation. The various fermentation methods such as surface, submerged and solid state were used for the production. In this book were discussed the various factors affecting the production rate, history of the production methods, microbial strains used for the production, biochemistry of the CA production by Aspergillus niger, production techniques and recovery process.