This entry is adapted from the peer-reviewed paper 10.3390/molecules28155739. Nanoparticles are defined as matter that has at least one dimension between 1 and 100 nm, and that generally has different properties from its bulk. This is particularly the case for metal nanoparticles, such as gold nanoparticles (NPs), which have a different color depending on their size and differs from the color of bulk gold, in connection with their surface plasmon resonance. Gold NPs are widely used for diagnostics and therapy. Dendrimers are monodisperse hyperbranched polymers of nanometric size, very different from classical polymers, as they are synthesized step-by-step and not by bulk polymerization reactions. Most dendrimers are synthesized by a divergent process, starting from a multifunctional core, possessing 2 to 8 functions in most cases. Such a divergent process frequently involves two steps. Among the different types of dendrimers, polyphosphorhydrazone (PPH) dendrimers have been chosen.