  Baryon-to-meson and baryon-to-photon transition distribution amplitudes
(TDAs) arise in the collinear factorized description of a class of hard
exclusive reactions characterized by the exchange of a non-zero baryon number
in the cross channel. These TDAs extend the concepts of generalized parton
distributions (GPDs) and baryon distribution amplitudes (DAs). In this review
we discuss the general properties and physical interpretation of
baryon-to-meson and baryon-to-photon TDAs. We argue that these non-perturbative
objects are a convenient complementary tool to explore the structure of baryons
at the partonic level. We present an overview of hard exclusive reactions
admitting a description in terms of TDAs. We discuss the first signals from
hard exclusive backward meson electroproduction at JLab with the 6 GeV electron
beam and explore further experimental opportunities to access TDAs at JLab@12
GeV, PANDA and J-PARC.
