Essential oils (EOs) have been long recognized for their antibacterial, antifungal and antiviral properties. They are widely used in medicine for these purposes. The increased interest in alternative natural substances is driving the research community to find new uses and applications of these substances. EOs and their components show promising activities against many pathogens and spoilage microorganisms when tested in vitro. The use of combinations of EOs and their isolated components are thus new approaches to increase the efficacy of EOs in microorganisms control, taking advantage of their synergistic and additive effects. The purpose of this review is to survey of the methods used for the determination EOs activity by gaseous contact and mechanisms involved in the antimicrobial activities are also reported. EOs and their volatile constituents are used widely to prevent and treat human diseases. The possible role and mode of action of these natural products are discussed, as well as their bioactivity as antimicrobial agents. Their application as natural products enhanced drug delivery and the therapeutic properties of essential oils in aroma therapy will also be outlined. Their antimicrobial properties and low toxicity make them ideal as additives in food, cleaning products, medicine aromatherapy.