Despite the large progress in medicine and pharmacy in the last few decades, traditional treatment of bacterial or viral diseases is frequently ineffective and is connected with some side effects. Currently, there is observed an increasing interest in natural plant-derived substances as a potential and promising group of medicines in prevention and treatment of several infectious diseases. Terpenes and their derivatives are a large class of natural organic components of essential oils and are widespread in the plant kingdom. Numerous experimental studies have shown that essential oils exhibit a large spectrum of biological and pharmacological activities in vitro. Herbal essential oils have been proved to possess antimicrobial, antiviral, antifungal and antiparasitic properties. They have also been reported to exhibit anti-inflammatory and immunostimulatory activities. Based on the wide spectrum of various biological activities, essential oils and terpenes commonly found in fruit, vegetables, herbs etc. have been suggested to constitute a novel group of preventive and therapeutic agents. Further experiments are necessary to confirm their pharmacological effectiveness, to determine potential toxic effects and the mechanism of their activity in in vivo models. This article describes the biological and pharmacological properties of herbal essential oils and some of their components, and summarizes the future prospects of potential application of essential oils in the prevention and treatment of infectious human diseases. In this review also possible mechanisms of their biological action are presented.