Neutron Compton scattering measurements have the potential to provide
direct information about atomic momentum distributions and adiabatic e
nergy surfaces in condensed matter. First applied to measuring the con
densate fraction in superfluid helium, the technique has recently been
extended to study a variety of classical and quantum liquids and soli
ds. This article reviews the theoretical background for the interpreta
tion of neutron Compton scattering, with emphasis on studies of solids
.