Volume 6 of Atomic and Plasma–Material Interaction Data for Fusion includes critical reviews and results of original experimental and theoretical studies on inelastic collision processes among the basic and dominant impurity constituents of fusion plasmas. The following processes are considered: electron impact excitation of excited helium atoms, electron impact excitation and ionization of plasma impurity ions and atoms, electron–impurity–ion recombination and excitation, ionization and electron capture in collisions of plasma protons and impurity ions with the main fusion plasma neutron components H, He and H2 (the latter being always present in the plasma edge or introduced into the plasma by neutral beam injection for heating, fuelling or diagnostic purposes).