This review summarizes the chemical composition and biological activities of essential oils, focusing on their antioxidant, antimicrobial, anti-inflammatory, and cancer chemoprotective properties. Essential oils are complex mixtures of volatile compounds, mainly terpenes and phenolic compounds, derived from aromatic plants. They have a wide range of biological activities, including antioxidant, anti-inflammatory, antimicrobial, and cytotoxic effects, which make them valuable in food, cosmetic, and pharmaceutical industries. The review discusses the chemical pathways involved in the biosynthesis of essential oils, highlighting the mevalonate and shikimate pathways. The composition of essential oils varies based on factors such as plant species, growth conditions, and extraction methods. The biological activities of essential oils are influenced by their chemical composition, with compounds like thymol, carvacrol, and eugenol showing significant antimicrobial and antioxidant properties. The review also explores the synergistic and antagonistic effects of essential oil combinations, as well as their potential applications in agriculture and medicine. Overall, essential oils offer promising alternatives to synthetic compounds due to their natural origin and diverse biological activities.This review summarizes the chemical composition and biological activities of essential oils, focusing on their antioxidant, antimicrobial, anti-inflammatory, and cancer chemoprotective properties. Essential oils are complex mixtures of volatile compounds, mainly terpenes and phenolic compounds, derived from aromatic plants. They have a wide range of biological activities, including antioxidant, anti-inflammatory, antimicrobial, and cytotoxic effects, which make them valuable in food, cosmetic, and pharmaceutical industries. The review discusses the chemical pathways involved in the biosynthesis of essential oils, highlighting the mevalonate and shikimate pathways. The composition of essential oils varies based on factors such as plant species, growth conditions, and extraction methods. The biological activities of essential oils are influenced by their chemical composition, with compounds like thymol, carvacrol, and eugenol showing significant antimicrobial and antioxidant properties. The review also explores the synergistic and antagonistic effects of essential oil combinations, as well as their potential applications in agriculture and medicine. Overall, essential oils offer promising alternatives to synthetic compounds due to their natural origin and diverse biological activities.