  The roles of the Drell-Yan experiments in studying the
Transverse-Momentum-Dependent (TMD) parton distributions are discussed. Recent
results from the Fermilab E866 experiment on the angular distributions of
Drell-Yan dimuons in $p+p$ and $p+d$ at 800 GeV/c are presented. These data are
compared with the pion-induced Drell-Yan data, and with models which attribute
the $\cos 2 \phi$ azimuthal distribution to the presence of the
transverse-momentum-dependent Boer-Mulders structure function $h_1^\perp$.
Constraints on the magnitude of the sea-quark $h_1^\perp$ structure functions
are obtained. Future prospects for studying the TMDs with Drell-Yan experiments
at Fermilab and J-PARC are also discussed.
