In recent years, it has become possible to inhibit constitutive production of biogenic volatile organic compounds (BVOC) in trees by genetic engineering. In addition, the trait for constitutive emissions has been introduced in several previously non-emitting herbaceous model organisms and crops. Research on these genetically engineered organisms has demonstrated that eliminating terpenes (syn. terpenoids or isoprenoids) emission reduces stress tolerance, while enhancing emissions often increases abiotic and biotic stress tolerance. In this chapter, the progress in terpene engineering work is reviewed, and the advantages of, changes in and obstacles related to genetically modified (GM) trees are discussed. We start by introducing the reader to terpene biosynthesis and the efforts undertaken to manipulate that process, we further review past attempts to repress and overexpress terpene synthases in herbs and trees, and finally describe the current achievements and suggest future possibilities in the field of terpene emission engineering.