Plasmonic modes confined to metallic nanostructures at the atomic and molecular scale push the boundaries of light-matter interactions. Within these extreme plasmonic structures of ultrathin nanogaps and tunnelling junctions, new physical phenomena arise when plasmon resonances couple to electronic, exitonic, or vibrational excitations, as well as the generation of non-radiative hot carriers. This thesis will summarize experimental and theoretical advances in the regime of extreme nanoplasmonics, with an emphasis on plasmon-induced hot carriers, strong plexitonic effects, and electrically driven processes at the molecular scale. We examine above-threshold light emission in electromigrated tunnel junctions, which is consistent with a suggested theoretical model describing hot-carrier dynamics driven by nonradiative decay of electrically excited localized plasmons. By progressively altering the tunneling conductance of an aluminum junction, we tune the dominant light emission mechanism through different possibilities for the first time, finding quantitative agreement with theory in each regime. Using plasmonic tunnel junctions as a platform supporting both electrically and optically excited localized surface plasmons, we report a much greater (over 1000× ) plasmonic light emission at upconverted photon energies under combined electro-optical excitation, compared with electrical or optical excitation separately. We use electroluminescence to probe plasmon-exciton coupling in hybrid structures each consisting of a nanoscale plasmonic tunnel junction and few-layer two-dimensional transition-metal dichalcogenide transferred onto the junction. The resulting hybrid states act as a novel dielectric environment to affect the radiative recombination of hot carriers in the plasmonic nanostructure. Further potential of this work and possible future research directions will also be discussed.