  Electromagnetic reactions on light nuclei are fundamental to advance our
understanding of nuclear structure and dynamics. The perturbative nature of the
electromagnetic probes allows to clearly connect measured cross sections with
the calculated structure properties of nuclear targets. We present an overview
on recent theoretical ab-initio calculations of electron-scattering and
photonuclear reactions involving light nuclei. We encompass both the
conventional approach and the novel theoretical framework provided by chiral
effective field theories. Because both strong and electromagnetic interactions
are involved in the processes under study, comparison with available
experimental data provides stringent constraints on both many-body nuclear
Hamiltonians and electromagnetic currents. We discuss what we have learned from
studies on electromagnetic observables of light nuclei, starting from the
deuteron and reaching up to nuclear systems with mass number A=16.
