Future polarized Drell-Yan experiments - probing hadron structure

The study of Drell-Yan (DY) processes involving the collision of an (un)polarised hadron beam on an (un)polarised (proton) target can result in a fundamental improvement of our knowledge on the transverse momentum dependent (TMDs) parton distribution functions (PDFs) of hadrons. The production mechanism of $J/\psi$ and $J/\psi$ - DY duality can also be addressed. The future polarised COMPASS DY experiment is discussed in this context, the most important features briefly reviewed.