Essential oils (EOs) are widely used in the perfume, cosmetic, pharmaceutical, agricultural, and food industries. These have long been recognized since antiquity to possess biological activities, including antioxidant, antibacterial, antifungal, antiviral, antimycosic, antitoxigenic, antiparasitic, and insecticidal properties. In recent years, a large number of EOs and their constituents have been investigated for their food preservation. This chapter presents an overview of the antioxidant and antimicrobial activities of different EOs for the preservation of food products. It provides the necessary theoretical background about the antioxidant and antimicrobial activities and the common analytical techniques to assess them. Applications of EOs as food antioxidants and antimicrobials are presented.