The object of the paper is to present a nonlocal theory of disperse systems of chemical engineering, formulated in terms of a generalized population balance equation, allowing for describing both continuous and noncontinuous, mono- and multiparticle events. By imposing different conditions on the constitutive functions, one can obtain in a systematic manner a variety of common models for disperse systems, corresponding to either batch, semi-batch or continuous unit operations. The theory is illustrated by presenting an example of obtaining models for mixing processes of fluids.