Interactions between plasma and neutral matter in the magnetosphere of Saturn can be classified by whether or not they entail reactions which change the charge or atomic state of the particle. Charge exchange and ion-atom interchange are examples of the first type while isotropizing and thermalizing collisions are examples of the second kind. A third type of interaction is that between magnetospheric charged particles and the surface layers of the icy satellites or the upper atmosphere of Titan, which results in sputtering of the surface or atmosphere and the injection of the neutrals into the magnetosphere. Interaction with ice motes appears to be less important. Dissociative recombination is, stricto sensu, an interaction between charged particles, but it is a major sink for plasma and a prime source of the neutral wind. The roles and effects of these various types of interactions as they manifest themselves in the phenomenology observed in the various regions of the magnetosphere of Saturn are surveyed in this review. Constraints supplied by known reaction rates provide a means of evaluating the abundance of the various members of the water group family. An hypothesis for resolving discrepancies in the interpretation of various Voyager data sets is proposed.