Silicon nanowires (Si-NWs) represent useful building blocks for nanoelectronic de-vices in many fields such as photovoltaics, photocatalysis, sensing or photodetectors. This is because they show interesting optical properties, including plasmon resonance (PR), the collective oscillation of free electrons, induced by an electromagnetic field at the proper frequency. PR is a versatile phenomenon because it is tunable depending on the intended application by modulating the nanosystem geometry, the medium cover-ing or surrounding it and its shape. It allows, for example, to use Si-NWs to collect and amplify, by several orders of magnitude, radiant energy by generating a locally ampli-fied electric field, a beneficial mechanism in many applications. Till now, however, there are no direct observations neither deep understanding in the literature on PR in Si-NWs. In this talk, the surface plasmon resonances triggered in isolated Si-NWs with diameters below than 100 nm are visualized at high spatial resolution. We characterize the systems through transmission electron microscopy (TEM) coupled to electron en-ergy loss spectroscopy (EELS) with a subnanometer electron probe. The plasmon be-havior of the SiNWs is then modeled through theoretical calculations, and the results are in good agreement with the experimental data. The electrical field spatial distribu-tion generated by the PR is mapped and rationalized. As an extension of our study, we show experimental, and modeling data on SiNWs coated with different materials and structures, and we compare the plasmonic behavior to the one of pristine SiNWs.