This review focuses on the molecular biology and phylogenetic analysis of plant terpenoid synthases, which are enzymes that catalyze the synthesis of monoterpene, sesquiterpene, and diterpene terpenoids. The enzymology and mechanism of terpenoid cyclization are described, along with the molecular cloning and heterologous expression of these enzymes. Sequence-relatedness and phylogenetic reconstruction based on 33 members of the Tps gene family are discussed, and the structural features of these enzymes are compared. The review also covers the organization and regulation of terpenoid metabolism and the biotechnological applications of terpenoid synthase genes. Monoterpene, sesquiterpene, and diterpene synthases use prenyl diphosphate substrates to generate diverse carbon skeletons, with the synthases being highly specific for their respective substrates. The review highlights the similarities in the reaction mechanisms among these enzymes and their roles in plant defense and secondary metabolism.This review focuses on the molecular biology and phylogenetic analysis of plant terpenoid synthases, which are enzymes that catalyze the synthesis of monoterpene, sesquiterpene, and diterpene terpenoids. The enzymology and mechanism of terpenoid cyclization are described, along with the molecular cloning and heterologous expression of these enzymes. Sequence-relatedness and phylogenetic reconstruction based on 33 members of the Tps gene family are discussed, and the structural features of these enzymes are compared. The review also covers the organization and regulation of terpenoid metabolism and the biotechnological applications of terpenoid synthase genes. Monoterpene, sesquiterpene, and diterpene synthases use prenyl diphosphate substrates to generate diverse carbon skeletons, with the synthases being highly specific for their respective substrates. The review highlights the similarities in the reaction mechanisms among these enzymes and their roles in plant defense and secondary metabolism.