  The concept of the potential acting between charged particles is reviewed
within the framework of quantum electrodynamics. The one-photon and two-photon
exchange potentials V_1 \gamma and V_2 \gamma are discussed, with attention to
the following features: the dependence of V_2 \gamma on the choice of V_1
\gamma, the distinction between FGI (Feynman gauge inspired) and CGI (Coulomb
gauge inspired) potentials, and the dependence of the large-r behavior on these
choices. A summary of available results for two spin-0 particles, for a spin-0
and a spin 1/2 particle and for two spin-1/2 particles is given. The
application of such "scattering potentials" to the calculation of energy levels
of bound states is discussed.

High Energy Physics - Phenomenology