  A review of the main phenomena related with the linear optical properties of
isolated and supported metal nanoparticles is presented. The extinction,
absorption and scattering efficiencies are calculated using the Mie theory and
the Discrete Dipole Approximation. The origin of the optical spectra is
discussed in terms of the size, shape and environment for each nanoparticle.
The main optical features of each nanoparticle are identified, showing the
tremendous potentiality of optical spectroscopy as a tool of characterization.
