Nonconventional medium for biocatalysis can enable complementary advantages to catalyze reactions. Deep eutectic solvents, a class of neoteric media, are inexpensive and easy to prepare, inherently biodegradable and nonvolatile, and can be applied to both whole cells and isolated enzyme-catalyzed transformations. Their role in synthetic transformations is reviewed in this chapter, focusing on their capability to induce different reactivities, enhance substrate solubility and stabilize enzymes, spanning from single transformations involving hydrolases to oxidoreductases, transferases and lyases, but also considering multistep transformations involving metal-enzyme and organocatalyst-enzyme combinations.