Interactions between drug particulates are crucial in determining drug dispersion and deaggregation, and ultimately delivery efficiency. This book combines principles established in surface and colloidal chemistry with pharmaceutical powder technology. It discusses some of the factors affecting particulate interactions, and particle-fluid interaction in the respiratory tract. The book then goes on to critically review some of the studies carried out in dry powder formulation development, and finally, it proposes possible strategies in improving DPI efficiency. The majority of these principles are applicable to other pharmaceutical solid dosage forms (e.g. tablets and capsules).