There is a great worldwide demand for citric acid consumption due to its low toxicity when compared with other acidulants used mainly in the pharmaceutical and food industries. Other applications of citric acid can be found in detergents and cleaning products, cosmetics and toiletries, and other. Global production has now reached 1.4 million tonnes and there is annual growth of 3.5–4.0% in demand/consumption of citric acid. As a result of the adverse market conditions, only big producers have survived. Any increase in citric acid productivity would be of potential interest and hence there is an obvious need to consider all possible ways in which this might be achieved. The production by submerged fermentation is still dominating. However, solid-state processes can create new possibilities for producers. Many by-products and residues of the agro-industry can be used in the production of citric acid. A cost reduction in citric acid production can be achieved by using less expensive substrates. The use of agro-industrial residues as support in solid-state fermentation is economically important and minimizes environmental problems. Other perspectives for citric acid production sector are the improvement of citric acid producing strains, which have been carried out by mutagenesis and selection.