Book excerpt: Terpenes belong to the diverse class of chemical constituents isolated from materials found in nature (plants, fungi, insects, marine organisms, plant pathogens, animals and endophytes). These metabolites have simple to complex structures derived from Isopentyl diphosphate (IPP), dimethyl allyl diphosphate (DMAPP), mevalonate and deoxyxylulose biosynthetic pathways. Terpenes play a very important role in human health and have significant biological activities (anticancer, antimicrobial, anti-inflammatory, antioxidant, antiallergic, skin permeation enhancer, anti-diabetic, immunomodulatory, anti-insecticidal). This book gives an overview and highlights recent research in the phytochemical and biological understanding of terpenes and terpenoid and explains the most essential functions of these kinds of secondary metabolites isolated from natural sources.