Hard exclusive processes are central in order to get access to the three-dimensional
structure of hadrons in terms of quarks and gluons. We review their modern
theoretical background. The collinear factorization approach is presented and illustrated,
including deep virtual Compton scattering (DVCS), non-exotic and exotic meson
electroproduction. We focus in particular on the threshold resummation effects
involved in the DVCS coefficient functions. To illustrate the problem of dealing with
power corrections to the scattering amplitudes, we consider
the chiral-odd pion generalized parton distributions up to twist 5. We then provide a
short survey of kt-factorization in the limit of asymptotical center-of-mass energies.
This is further illustrated by the study of power corrections and saturation effects in
exclusive vector meson electroproduction at HERA, of interest in view of the future
EIC and LHeC projects.