In nature, enzymes traditionally work under aqueous conditions. For this reason, aqueous buffers are often the preferred reaction medium when enzymes are used in chemical synthesis. However, in order to meet the requirements of an industrial application, an aqueous reaction system will often not be able to provide sufficient substrate loadings due to the poor water solubility of many industrially relevant compounds. Switching to a non-aqueous solvent system can provide a solution that is already common for lipases but is more challenging for biocatalysts of other enzyme classes. However, the choice of solvent types and systems can be overwhelming. In addition, some engineering of the protein structure of the biocatalyst formulation is required. This Review provides a guide for those who work with biocatalysts and are looking for a way to increase their reaction productivity. The examples reported clearly show that no amount of water is required for biocatalytic reactions and that a clever design of solvent systems can support increased product concentrations and thereby reduce waste generation. In addition, under these conditions enzymes can also be combined in cascades with other water-sensitive chemical catalysts. Finally, we show that the use of non-aqueous solvents in biocatalysis can actually lead to more sustainable processes. Using flowcharts, you can quickly find out which solvent systems are feasible after asking simple questions.