Esters represent one of the most important classes of aroma compounds in fruits, fermented foods, and beverages and are responsible for their floral notes. They play a key role in the definition of the aroma of several fruits such as apples and strawberries. Some esters can be associated with specific fruits: 3-methylbutyl acetate is characteristic of pear, allyl hexanoate is present in pineapple, and the C9 esters are important for melon aroma. Moreover, they are responsible for the aroma of cured ham and cheeses. In wine they are responsible for fruity notes. However, they can also have other applications in addition to flavor such as cosmetics, pharmaceuticals, green solvents, and advanced biofuels. In this chapter the main metabolic pathways involved in ester production and degradation in yeasts and bacteria are reported. Moreover, the role of yeasts, filamentous fungi, and bacteria in the formation of esters in wine and cheese is explored in depth.