The peculiar features of theory in the field of Particle Technology are discussed by an analysis of three different situations. In the theory of yield of cohesive powders, experimental and theoretical results obtained from single particle experiments are unified in order to generate a physical, i.e. not phenomenological theory of the yield of cohesive powders. The second example of this paper provides evidence that theory in the form of a structural analysis is a useful tool for finding better-suited variants of dimensionless groups for use in particle technology. The third example is devoted to the pneumatic transport of coarse-grained particles in horizontal pipes. This topic has been chosen due to two significant features. With strand flow conveying close to the plugging limit. an indirect interaction is observed in the form of A provides B, and B provides C. The second aspect is rather the norm than the exception in particle technology: the range of possible operational conditions is so broad, that in different regimes, different mechanisms prevail. This fact largely impedes the success of purely empirical approaches.