  In this chapter we analyze the multiple ionization by impact of |Z|=1
projectiles: electrons, positrons, protons and antiprotons. Differences and
similarities among the cross sections by these four projectiles allows us to
have an insight on the physics involved. Mass and charge effects, energy
thresholds, and relative importance of collisional and post-collisional
processes are discussed. For this purpose, we performed a detailed
theoretical-experimental comparison for single up to quintuple ionization of
Ne, Ar, Kr and Xe by particles and antiparticles. We include an extensive
compilation of the available data for the sixteen collisional systems, and the
theoretical cross sections by means of the continuum distorted wave eikonal
initial state approximation. We underline here that post-collisional ionization
is decisive to describe multiple ionization by light projectiles, covering
almost the whole energy range, from threshold to high energies. The
normalization of positron and antiproton measurements to electron impact ones,
the lack of data in certain cases, and the future prospects are presented and
discussed.
