Plants use natural products called terpenes as part of their chemical response to environmental stresses. Legume species represent important agricultural and feed crops that are known to produce terpene-based compounds when under herbivore or microbial stress but whose defense mechanisms are not well understood. We worked to better elucidate the biosynthetic pathways behind terpene biosynthesis through characterization of terpene synthases (TPSs) in the model legume Medicago truncatula. Our characterization efforts focused on TPSs in terpene clades TPS-a and TPS-b, which includes monoterpene (C10) and sesquiterpene (C15) synthases with products often used in herbivore or microbial defense. We characterized several TPSs through co-expression with their predicted substrates and found several of them produced known antiherbivore or antimicrobial products. Treatments with methyl jasmonate or salicylic acid meant to mimic herbivore and microbial stress responses caused an increase in expression of several TPSs in planta, supporting potential defensive roles. Our characterization of biosynthetic enzymes and evaluation of their expression in M. truncatula allows for better understanding of legume chemical response strategies.