Cofactor-dependent enzymes catalyze a broad range of synthetically useful transformations. However, the cofactor requirement also poses economic and practical challenges for the application of these biocatalysts. For three decades, considerable research effort has been devoted to the development of reliable in situ regeneration methods for the most commonly employed cofactors, particularly NADH and NADPH. Today, researchers can choose from a plethora of options, and oxidoreductases are routinely employed even on industrial scale. Nevertheless, more efficient cofactor regeneration methods are still being developed, with the aim of achieving better atom economy, simpler reaction setups, and higher productivities. Besides, cofactor dependence has been recognized as an opportunity to confer novel reactivity upon enzymes by engineering their cofactors, and to couple (redox) biotransformations in multi-enzyme cascade systems. These novel concepts will help to further establish cofactor-dependent biotransformations as an attractive option for the synthesis of biologically active compounds, chiral building blocks, and bio-based platform molecules.