  We discuss the angular distribution of the lepton pair in the Drell-Yan
process, hadron+hadron -> \gamma^* X -> l^+ l^- X. This process gives
information on the spin-density matrix \rho^{(q,\bar{q})} of the annihilating
quark-antiquark pair in q+\bar{q} -> l^+ l^-. There is strong experimental
evidence that even for unpolarised initial hadrons \rho^{(q,\bar{q})} is
nontrivial, and therefore the quark-antiquark system is polarised. We discuss
the possibilities of a general \rho^{(q,\bar{q})} -which could be entangled-
and a factorising \rho^{(q,\bar{q})}. We argue that instantons may lead to a
nontrivial \rho^{(q,\bar{q})} of the type indicated by experiments.
