  A mean-field model with a generalized pairing interaction that accounts for
neutron-proton pairing is presented. Both the BCS as well as number-projected
solutions of the model are presented. For the latter case the Lipkin-Nogami
projection technique was extended to encompass the case of non-separable
proton-neutron systems. The influence of the projection on various pairing
phases is discussed. In particular, it is shown that number-projection allows
for mixing of different pairing phases but, simultanously, acts destructively
on the proton-neutron correlations. The basic implications of proton-neutron
pairing correlations on nuclear masses are discussed. It is shown that these
correlations may provide a natural microscopic explanation of the Wigner energy
lacking in mean-field models. A possible phase transition from isovector to
isoscalar pairing condensate at high angular momenta is also discussed. In
particular predictions for the dynamical moments of inertia for the
superdeformed band in $^{88}$Ru are given.
