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Plants produce, with great structural and functional diversity, a remarkable array of phytochemicals (also recognized as specialized metabolites) which have significant roles in both plant development and defense responses. These phytochemicals may serve as a rich and important source of biologically active pharmaceuticals. While we learned a bunch about the biological activities of these compounds in relation to human health, little is known about how they are produced in plants. However, the biochemical evolution of terrestrial plants relies primarily on unique phenoxy-radical radical coupling reactions to establish different classes of chemical compounds. In this regard, the dirigent proteins (DIRs), a new class of proteins, controlling the stereoselectivity of these coupling processes in order to produce a wide range of natural products are unmatched. DIRs were discovered during 8-8′ lignan biosynthesis studies, through identification of stereoselective coupling to afford either (+)- or (−)-pinoresinols from the achiral precursor E-coniferyl alcohol. DIRs have very large multigene families in diverse vascular plants, including flax, most of which are still unknown for precise biochemical/physiological functions. DIRs are also involved or potentially involved in terpenoid, allyl/propenyl phenol lignan, pterocarpan and lignin biosynthesis. The DIRs ability to capture and orient radicals is also a unique naturally evolved concept for controlling radical dimerization reactions. While oxidative coupling is widely used in biological systems, its wider application in chemical synthesis is often impaired by insufficient selectivity. This presentation offers an overview of DIRs, their molecular and functional characteristics, and paves the way for their use in biotechnological applications.