Phytases are hydrolytic enzymes that initiate the release of phosphate from phytate (myo-inositol hexakisphosphate), the major phosphorus (P) form in animal feeds of plant origin. These enzymes can be supplemented in diets for food animals to improve P nutrition and to reduce P pollution of animal excreta. This minireview provides a synopsis of the concept of "ideal phytase" and the biotechnological approaches for developing such an enzyme. Examples of Escherichia coli AppA and Aspergillus fumigatus PhyA are presented to illustrate how new phytases are identified from microorganisms and developed by genetic engineering based on the gene sequences and protein structures of these enzymes. We also discuss the characteristics of different heterologous phytase expression systems, including those of plants, bacteria, fungi, and yeast.