Superconductivity, quasi-particle dynamics and strong-coupling physics

I discuss the problem of superconductivity from the perspective of pairing mediated by a boson and compare with the situation of ``no-glue'' superconductivity in a strongly correlated material. This is done for Tl-doped PbTe, where recent experiments support superconductivity due to quantum valence (charge Kondo) fluctuations, and for the doped Mott insulator SrCu$_{2}$(BO$_{3})_{2}$, where d-wave superconductivity emerges due to a reorganization of a valence bond crystal state. I discuss the implications of these results for high temperature superconductivity in the cuprates.