Fusion proteins, understood as those created by joining two or more genes that originally encoded independent proteins, have numerous applications in biotechnology, from analytical methods to metabolic engineering. The use of fusion enzymes in biocatalysis may be even more interesting due to the physical connection of enzymes catalyzing successive reactions into covalently linked complexes. The proximity of the active sites of two enzymes in multi-enzyme complexes can make a significant contribution to the catalytic efficiency of the reaction. However, the physical proximity of the active sites does not guarantee this result. Other aspects, such as the nature and length of the linker used for the fusion or the order in which the enzymes are fused, must be considered and optimized to achieve the expected increase in catalytic efficiency. In this review, we will relate the new advances in the design, creation, and use of fused enzymes with those achieved in biocatalysis over the past 20 years. Thus, we will discuss some examples of genetically fused enzymes and their application in carbon‑carbon bond formation and oxidative reactions, generation of chiral amines, synthesis of carbohydrates, biodegradation of plant biomass and plastics, and in the preparation of other high-value products.