This project has investigated the mechanism of caking of lactose and identified some possible solutions to minimise caking of lactose and dairy powders, additional to those suggested in the literature. A background to lactose and caking is given. The problems of caking are identified and discussed. The project adds information to the knowledge on the polymorphic forms of lactose and their inter-relationships due to moisture sorption and processes such as milling. This information and many others in the literature are used to complete the simplified lactose conversion diagram developed by King [1965] and improved by Walstra, et al. [1999], which has been widely used in the literature as a guide for lactose manufacturing, processing, and storage. / Doctor of Philosophy (PhD)