  Recent measurements of the deuteron electromagnetic structure functions A, B,
and $T_{20}$ extracted from high energy elastic $ed$ scattering, and the cross
sections and asymmetries extracted from high energy photodisintegration
$\gamma+d\to n+p$, are reviewed and compared to theory. The theoretical
calculations range from nonrelativistic and relativistic models using the
traditional meson and baryon degrees of freedom, to effective field theories,
to models based on the underlying quark and gluon degrees of freedom of QCD,
including nonperturbative quark cluster models and perturbative QCD. We review
what has been learned from these experiments, and discuss why elastic $ed$
scattering and photodisintegration seem to require very different theoretical
approaches, even though they are closely related experimentally.
