For several years now a growing number of experiments with pellet injection have been conducted on hot plasmas. So far different influences on the plasma performance have been reported. Strong peaking of the density profile is usually also seen in cases where the pellet does not penetrate to the centre. In ohmic discharges with sufficient edge recycling it was observed that the averaged density increases and in parallel the particle and energy confinement are substantially improved. With growing neutral injection power, this improvement degrades, while the central particle and energy confinement remain enhanced. The author presents a review of pellet injection work which only briefly summarizes the technical development and status of injectors. Ablation theory and comparison with experiments are also reported in condensed form. The author concentrates more on contributions to plasma confinement and reviews the most essential highlights of plasma experiments.