Amino acids are components of proteins in living organisms and exist not only as nutrients, energy sources, and taste/flavor components but also in free state within cells and plasma, where they play a variety of physiological functions. In recent years, their functions have been attracting attention, and many foods, beverages, supplements, pharmaceuticals, cosmetics, etc. with enhanced functionality by adding amino acids have been widely commercialized in the world. The budding yeast Saccharomyces cerevisiae is an important microorganism not only in basic biology but also in the fermentation industry. Amino acid metabolism and its regulatory mechanisms in yeast are diverse, and in basic science, the elucidation of these molecular mechanisms can deepen our understanding of biological phenomena and cellular functions. In the field of applied research, the artificial control of amino acid content inside and outside the cell is expected to lead to the production of amino acids themselves and metabolism-related substances, as well as fermented foods and alcoholic beverages with enhanced taste, flavor, health, and nutritional functions. We have established a breeding technology called “functional amino acid engineering” that artificially controls the content of “functional” amino acids, which can improve fermentation ability, diversify taste and flavor, impart a healthy image, and increase nutritional value, thereby developing high functionality of microorganisms and improving the productivity of useful substances.