  We review the status of electric/magnetic duality for free gauge field
theories in four space-time dimensions with emphasis on Maxwell theory and
linearized Einstein gravity. Using the theory of vector and tensor spherical
harmonics, we provide explicit construction of dual photons and gravitons by
decomposing the fields into axial and polar configurations with opposite parity
and interchanging the two sectors. When the theories are defined on AdS(4)
space-time there are boundary manifestations of the duality, which for the case
of gravity account for the energy-momentum/Cotton tensor duality (also known as
dual graviton correspondence). For AdS(4) black-hole backgrounds there is no
direct analogue of gravitational duality on the bulk, but there is still a
boundary duality for quasi-normal modes satisfying a selected set of boundary
conditions. Possible extensions of this framework and some open questions are
also briefly discussed.
