Friction is a very complex phenomenon: The sliding motion of surfaces in contact involves the continuous formation, deformation, and rupture of a multitude of microscopic contacts. With the invention of Friction Force Microscopy it became feasible to study these microscopic single-asperity contacts one by one. I will present some fundamental results on friction on the molecular scale. These will include a fascinating difference in friction between single layer and bilayer graphene grown epitaxially on SiC, which we compare to differences in the angle-resolved photoemission results. I will also discuss results on the incipient stages of plasticity in single crystals. Force microscopy not only detects the nucleation of single dislocations as a force drop during indentation, it also can image the corresponding structures at the surface, sometimes with atomic resolution.