One would expect fusion reactor design to be concerned principally with the primary reactants and spent fuel, that is the hydrogen and helium isotopes 2n, 3T and 4He, together with 7Li used for tritium breeding. Early plasma experiments conducted in devices of small dimension were however dominated by interaction of the plasma with the walls and the release of impurity species arising from this. In large machines, it was believed such problems would be reduced, but now, even in the Joint European Torus experiment, JET where the toroidal confinement vessel is 1-2 metres in minor radius, it has become evident that impurities sourced from the vessel walls and plasma contact points are hugely influential on plasma behaviour. Thus, the needs of cross-section data for fusion research are clearly focused on non-fuel as well as fuel species.