See the abstract given in Part I (Deliyannis, Pinsonneault, Charbonnel, hereafter DPC, this volume). In Part III, we first discuss the LiBeB observations in subgiant stars and the constraints they bring on the transport processes occuring on the main sequence. Evidence is then reviewed that suggests that in situ mixing occurs in evolved low mass Population I and Population II stars. Theoretical mechanisms that can create such mixing are discussed, as well as their implications for the evolution of the LiBeB and ³He.