Microbial citric acid is an important organic acid widely used in pharmaceutical food, beverage, detergents, and cosmetics industries. Although citric acid is produced by different types of microorganism, the filamentous fungus Aspergillus niger is a workhorse for the production of citric acid. In the present review, special attention has been paid to address the advanced literature of citric acid production such as microorganism, substrates, screening methods, different fermentation techniques, different factors affecting citric acid production, and product recovery as well as numerous biotechnological applications of citric acid are also discussed for simple understanding of the subject.