Plasmons—collective oscillations in the free electron plasma—constitute nanoscale optical resonators that are imbued with a nonlinear response by their supporting conductive media. In the 2D limit represented by atomically thin materials, plasmon resonances provide unprecedented levels of optical field confinement, while exhibiting relatively lower losses in pristine samples. The appealing properties of 2D plasmons are ideal for nonlinear plasmonics, which seeks to overcome the weak nonlinear response of available materials by exploiting the large near field enhancement supplied by plasmon resonances. Here we theoretically explore nonlinear light-matter interactions of 2D plasmons hosted in atomically thin materials and their heterostructures. Our investigations are based on nonclassical methods to describe graphene plasmons , characterized by high confinement and electrical tunability, plasmons supported by ultrathin crystalline noble metal films , with thickness-dependent properties and lower losses than their amorphous counterparts, and nanostructured phosphorene , an anisotropic two-dimensional semiconductor that hosts plasmons in highly-doped samples. We further explore possibilities to trigger nonlinear interactions on the few-plasmon level  and to enhance harmonic generation through synergetic interactions between plasmons in atomically-thin heterostructures .