This work is devoted to the study of the optical properties of semiconductor and metallic nanostructures. The inelastic light scattering by low frequency acoustic vibrations (AV), called Raman-Brillouin (RB) scattering, gives access to such properties. The confined electronic states of semiconductor nanostructures are involved in the RB scattering as an intermediary. When applying an external electric field, metallic nano-objects sustain collective oscillation modes of the free electron gas (plasmons) which also act as an intermediary during the emission and the absorption of low frequency AV in the RB scattering process. The understanding of the interaction between the AV and the electronic excitations (excitons or plasmons) gives direct information on the optical and vibrational properties of those nano-objects. New physical concepts are introduced as theoretical tools for the interpretation of the RB scattering in semiconductors and metals. An effective electronic density, responsible for the RB scattering in semiconductors, is here introduced for the first time as new advanced theoretical tool for the interpretation of the inelastic light scattering processes by low frequency AV. The concept of acousto-plasmonics is also introduced for the first time to study and describe the modulation of the plasmonic properties of metallic nano-objects by the AV. These concepts and the numerical methods used in this work (BEM, DDA, FDTD) allowed to interpret fine physical effects such as significant spectral red-shifts of plasmons resonances and unexpected observations of AV by RB spectroscopy.