  Light beams can be symmetric under different transformations: translations,
rotations, mirror symmetries, duality transformations, etc. In this thesis, a
systematic way of characterizing these symmetries is presented. Then, it is
shown that light beams symmetric under different transformations can be used to
control light-matter interactions at the nano-scale. Particular applications
are developed, both theoretically and experimentally. Inducing a dual behaviour
on a non-dual sample, the excitation of high multipolar order resonances and
the measurement of circular dichroism using vortex beams are among them.
