  The general properties of antiproton-proton annihilation at rest are
presented, with special focus on the two-meson final states. The data exhibit
remarkable dynamical selection rules : some allowed annihilation modes are
suppressed by one order of magnitude with respect to modes of comparable
phase-space. Various phenomenological analyses are reviewed, based on
microscopic quark dynamics or symmetry considerations. The role of initial- and
final-state interaction is also examined.
