  Polarization observables for the A(e,e'NN) and A(\gamma,NN) reactions are a
powerful tool to study nucleon-nucleon correlations in the nuclear medium. In
this paper, model calculations for the ^{4}He(e,e'pp),
^{16}O(\vec{e},e'\vec{p}p), ^{16}O(\vec{e},e' \vec{p}n) and
^{12}C(\vec{\gamma},\vec{p}N) reactions are presented. The sensitivity of the
differential cross sections and polarization observables to central and
spin-dependent nucleon-nucleon correlations is discussed.
