  The diverse community of scientists involved in Deep Inelastic Scattering
includes about 2000 experimental and theoretical physicists worldwide and
envisages projects such as the EIC, LHeC, FCC-eh and VHEeP as future
lepton-hadron scattering facilities. The proposed facilities will address
fundamental questions in strong interaction / QCD physics, including a
first-ever tomographic mapping of the hadrons' internal structure, a solution
to the proton mass and spin problems, understanding of the high-energy
structure of hadronic matter and insight into connections between gravity and
the strong interactions. They also extend and enhance the CERN programme of
searches for new physics at the energy frontier, through a standalone precision
Higgs and top programme, considerable sensitivity to the direct production of
new particles and the most precise determinations of proton and nuclear
structure in the kinematic range that is relevant to the LHC. In particular, we
highlight the complementary aspects of the different lepton-hadron projects,
and underscore how all are required to provide a complete characterization of
the physics across the full kinematic reach. This review of the proposed
facilities and their vast potential for particle physics was inspired by the
discussions in the 2018 "DIS and Related Subjects" Workshop.
