Terpenes are secondary metabolites produced by plants and they have promising roles in plant defense and pharmaceuticals. They are synthesized by terpene synthases and these enzymes are part of a complex plant metabolic pathway. Diterpene biosynthesis requires co-expression of class II and class I diterpene synthases (diTPSs) to convert geranylgeranyl diphosphate (GGPP), the common precursor, into a C20 intermediate substrate. These substrates then use cytochrome p450s (CYPs) as their final steps to form diterpene scaffolds. CYPs are monooxygenases that change the redox status of their substrates into final diterpene products. Medicago truncatula was used as my model organism to investigate how legumes synthesize these secondary metabolites to contribute to crop defense improvement in the future. Seven diTPSs - MtTPS17, MtTPS18, MtTPS19, MtTPS37, MtTPS38, MtTPS39, and MtTPS40 - in M. truncatula have been identified. MtTPS38 was found to produce ent-CPP and MtTPS37 used ent-CPP to yield ent-kaurene. Combinatorial expression showed that MtTPS38 and MtTPS37 react together to produce ent-kaurene, a precursor for an important plant hormone gibberellin (GA). CYPs have also been discovered to be clustered around MtTPS19, suggesting the possibility of MtTPS19 utilizing these CYPs for downstream reactions.