The (e,2e) technique has been applied to the problem of direct outer s
hell ionization for many years, with considerable success. In recent y
ears an increasing number of groups have explored the process of inner
shell ionization, with a view to obtaining information on the dynamic
s of the process. In this paper, the existing theoretical and experime
ntal studies of this process are discussed. Our recent measurements of
the triple differential cross section for 2p ionization in argon, per
formed at lower energies than have been used previously, are presented
.