The role of dopants in processing ceramics has been an important issue for many years, especially given the contradicting reports of retarded or accelerated grain growth due to the presence of dopants and/or impurities. For polycrystalline alumina, Mg is used to retard grain growth, while Ca has been thought to cause an increase in grain growth kinetics. New analysis of the grain boundary grain boundary mobility of alumina as a function of dopant concentration has shown that some segregating dopants increase the grain boundary mobility (at concentrations below the solubility limit), i.e. the opposite of the known solute-drag effect. The segregating dopants are associated with 2-D structural and compositional transitions at the grain boundaries, and possible changes in the mechanism of grain boundary migration, leading to “solute acceleration”. This presentation will review recent grain boundary mobility measurements, the concept of 2-D grain boundary transitions, and their potential role on the mechanism of grain boundary motion. The influence of “solute acceleration” in the presence of Zener drag inducing second phase particles will also be discussed.