Dendrimers are nanometric macromolecules constituted of repetitive branched units, arranged radially around a central core. They are synthesized step-by-step, generally using a divergent process from this core. Dendrimers have many properties and, among them, catalysis is a major field. Two main area are studied, on the one hand the search for a positive “dendrimer effect,” i.e. an increase in catalytic efficiency when the size of the dendrimer increases, and on the other the encapsulation of catalytically active nanoparticles inside dendrimers. In both cases, noncovalent interactions are involved. This chapter discusses the important role played by noncovalent interactions in the properties of dendrimers in catalysis. The first part concerns the dendrimer effect, then a short section considers noncovalently formed catalytic dendrimers and the final part concerns dendrimers encapsulating catalytic nanoparticles.