Essential oils are natural compounds obtained from plants with powerful biological activities. Several studies have reported their use as food additives due to their actions as antimicrobial and antioxidant agents. Despite some limitations, such as aroma and toxicity related to high doses, the use of essential oils in foods is promising and makes it possible to reduce the use of synthetic additives in food applications. In this chapter, the most common extraction methods, as well as the antioxidant and antimicrobial activities of some essential oils are addressed. The legal aspects and the general health effects of essential oils are also covered.