After the seminal catalytic studies carried out with crown ethers and cryptands, various other cage compounds have been used including cyclophanes, cyclodextrins, calixarenes, cucurbiturils, Zn-porphyrin macrocycles, cavitands, capsules composed of resorcinarenes, carcerands or tetrahedral assemblies, surfactant-based micelles and vesicles, and more recently dendrimers used as unimolecular micelles and yolk-shell or nanorattle structures. A large number of catalytic reactions has been performed with increased yields and selectivities compared to analogous reactions conducted in the absence of nanoreactors. The amount of required catalyst for complete and selective substrate transformation can be as low as the ppm for several reactions as recently shown with “click” dendritic nanoreactors.