Hydrofunctionalisation represents a powerful approach for transforming simple unsaturated substrates into complex three-dimensional molecules. Achieving this requires precise control of regiochemistry and chemoselectivity, which can be facilitated by metal hydride catalysis. This lecture will highlight how structurally distinct cobalt hydrides can promote hydrofunctionalisation with contrasting selectivities via divergent mechanistic pathways. Visible-light irradiation can be harnessed to modulate selectivity[1,2] and also unlock new modes of reactivity,[3-8] thereby expanding the synthetic toolbox of cobalt-catalysed organic transformations.[1] Beltran, F.; Bergamaschi, E.; Funes-Ardoiz, I.; Teskey, C. J. Angew. Chem. Int. Ed. 2020, 59, 21176.[2] Bergamaschi, E.; Lunic, D.; Teskey, C. J. Angew. Chem. Int. Ed. 2022, 61, e202114482.[3] Bergamaschi, E.; Mayerhofer, V. J.; Teskey, C. J. ACS Catal. 2022, 12, 14806.[4] Qin, J.; Barday, M.; Jana, S.; Sanosa, N.; Funes-Ardoiz, I.; Teskey, C. J. Angew. Chem. Int. Ed. 2023, 62, e202310639[5] Mayerhofer, V. J.; Lippolis, M.; Teskey, C. J. Angew. Chem. Int. Ed. 2024, 63, e202314870.[6] Zhou, H.; Lunic, D.; Sanosa, N.; Sampedro, D.; Funes-Ardoiz, I.; Teskey, C. J. Angew. Chem. Int. Ed. 2025, 64, e202418869[7] S. Jana, D. A. Kusza, N. Vystavkin, D. Lunic, C. J. Teskey Chem. Sci. 2026,17, 1098-1104[8] J. Qin, L. Popek, M. Wyrtki, C. J. Teskey Angew. Chem. Int. Ed 2026, 65, e202525790