Nanocatalysts have triggered extensive research in academia and industry. The structural and surface properties of nanocatalysts improve the quality of products in many situations by controlling selectivity and reaction rates, while reducing the manufacturing cost. The key for nanocatalyst design is to ensure only the desired molecular interactions are accelerated. Typical examples of first generation catalysts are bimetallic platinum and zeolite catalysts. Recently, nanocatalysts have been extended to include more complex, designer structures such as dendrimers, microgels, polymer core–shells, carbon nanotubes, micelles, emulsions and liposomes. In this account, we briefly describe the early work on nanocatalysts, and discuss some of the modern developments of homogeneous and heterogeneous nanocatalysts and their relation to the field of nanoreactor technology.