  The state of the art concerning transverse-spin and transverse-momentum
phenomena in hard hadronic reactions is reviewed. An account is given of
single-spin and azimuthal asymmetries in semiinclusive deep inelastic
scattering, e^+ e^- annihilation, Drell-Yan production, and hadroproduction.
The ongoing experiments and the main theoretical frameworks are described in
the first part of the paper. The second part is devoted to the experimental
findings and their phenomenological interpretations. A brief discussion of the
perspectives of future measurements is finally presented.
