Description The proton is a complex composite object. Its structure, the dynamics of its constituents and its mass presently cannot be calculated from Quantum Chromo Dynamics without simplifying model assumptions. Momentum- and spin-dependent distributions of quarks and gluons have been determined with increasing precision through 50 years of deep inelastic lepton-proton scattering experiments and the QCD analysis of 30 years of high energy proton-proton collider data. Despite this significant effort, there remain important shortcomings in the knowledge of proton structure. The Drell-Yan process is a well-understood electromagnetic effect in which a beam-hadron quark/anti-quark annihilates with a target hadron anti-quark/quark. It is well suited to explore the sea quark structure of the proton, transverse momentum- and spin-dependent quark distributions (TMDs) and nuclear effects in proton quark structure. The seminar will briefly review the present knowledge of proton structure, introduce the Drell-Yan process and review current and future Drell-Yan experiments at CERN, FAIR, FNAL, J-PARC, NICA and RHIC, that aim to constrain TMDs, sea-quarks and nuclear effects. A focus of the talk will be future plans for Drell-Yan experiments with high-intensity meson and anti-proton beams at the CERN SPS.