Since the large-scale application of immobilized enzymes in the 1960s, substantial research efforts have aimed to optimize the structure of carrier materials for better catalytic efficiency. In this regard, nanoscale materials provide the upper limits in balancing the key factors that determine the efficiency of biocatalysts, including surface area, mass transfer resistance, and effective enzyme loading. Various nanomaterials, such as nanoparticles, nanofibers, nanotubes and nanoporous matrices, have shown potential for revolutionizing the preparation and use of biocatalysts. Beyond their high surface area:volume ratios, nanoscale biocatalyst systems exhibit unique behaviors that distinguish them from traditional immobilized systems. The Brownian motion of nanoparticles, confining effect of nanopores and self-assembling behaviors of discrete nanostructures are providing exciting opportunities in this field. The development of catalyst systems that are highly stable and efficient, capable of self-targeting or that function as molecular machines to catalyze multiple reactions is rapidly reshaping our vision of biocatalysts.