Essential oils of different species of the genus Ocimum are natural flavouring materials of commercial importance. The data given in current literature are pertaining to the chemical composition of essential oils of different Ocimum species viz., Ocimum basilicum Linn. (alt. Ocimum basilicum var. minimum, Ocimum basilicum var. purpurience), Ocimum campechianum Mill., Ocimum canum Sims. (Ocimum americanum), Ocimum citriodorum, Ocimum gratissimum Linn., Ocimum kilimandscharicum Linn., Ocimum micranthum Willd., Ocimum sanctum Linn., (alt. Ocimum tenuiflorum Linn.), Ocimum selloi Benth., Ocimum trichodon, Ocimum utricifolium from different geographical regions. A considerable difference in chemical composition of a particular species is found, which may be due to their occurrence in different eco-climatic zones and changes in edaphic factors. Attention is also focused on the biological properties of Ocimum oils which are related to their various interesting applications as antimicrobial, antioxidant, repellent, insecticidal, larvicidal, nematicidal and therapeutic (anti-inflammatory, antinociceptive, antipyretic, antiulcer, analgesic, anthelmintic, anticarcinogenic, skin permeation enhancer, immunomodulatory, cardio-protective, antilipidemic) agents.