This article reviews the molecular biology and phylogenetic analysis of plant terpenoid synthases, which are enzymes responsible for the biosynthesis of terpenoids, a diverse class of natural products. Terpenoid synthases catalyze the cyclization of prenyl diphosphates to generate a wide range of terpenoid structures, including monoterpenes, sesquiterpenes, and diterpenes. The review discusses the enzymology and mechanism of terpenoid cyclization, focusing on the role of GDP and GGDP as substrates, and the steps involved in their conversion to various terpenoid products. It also covers the molecular cloning and heterologous expression of these enzymes, highlighting the sequence relatedness and phylogenetic reconstruction of the Tps gene family. The article provides an overview of the organization and regulation of terpenoid metabolism, as well as the biotechnological applications of terpenoid synthase genes. The review emphasizes the structural and functional diversity of terpenoid synthases, their evolutionary relationships, and their roles in plant defense and secondary metabolism. It also discusses the structural features of these enzymes, including conserved amino acid residues and domains, and their implications for catalytic activity and substrate specificity. The article concludes with a perspective on the potential applications of terpenoid synthases in biotechnology, including the engineering of plant defenses and the modification of metabolic pathways for industrial and agricultural purposes.This article reviews the molecular biology and phylogenetic analysis of plant terpenoid synthases, which are enzymes responsible for the biosynthesis of terpenoids, a diverse class of natural products. Terpenoid synthases catalyze the cyclization of prenyl diphosphates to generate a wide range of terpenoid structures, including monoterpenes, sesquiterpenes, and diterpenes. The review discusses the enzymology and mechanism of terpenoid cyclization, focusing on the role of GDP and GGDP as substrates, and the steps involved in their conversion to various terpenoid products. It also covers the molecular cloning and heterologous expression of these enzymes, highlighting the sequence relatedness and phylogenetic reconstruction of the Tps gene family. The article provides an overview of the organization and regulation of terpenoid metabolism, as well as the biotechnological applications of terpenoid synthase genes. The review emphasizes the structural and functional diversity of terpenoid synthases, their evolutionary relationships, and their roles in plant defense and secondary metabolism. It also discusses the structural features of these enzymes, including conserved amino acid residues and domains, and their implications for catalytic activity and substrate specificity. The article concludes with a perspective on the potential applications of terpenoid synthases in biotechnology, including the engineering of plant defenses and the modification of metabolic pathways for industrial and agricultural purposes.