  A review is given of attempts to describe nuclear properties in terms of
neutron--proton pairs that are subsequently replaced by bosons. Some of the
standard approaches with low-spin pairs are recalled but the emphasis is on a
recently proposed framework with pairs of neutrons and protons with aligned
angular momentum. The analysis is carried out for general $j$ and applied to
$N=Z$ nuclei in the $1f_{7/2}$ and $1g_{9/2}$ shells.
