Applied economics consists of the application of the general principles of economics to a particular situation in order to provide an explanation of the behavior of economic agents in that situation. However, the degree of specificity of any explanation depends upon the particular uses to which the explanation is to be put. Thus, in applied economics one may wish to explain the behavior of the agents who operate a particular enterprise. Or, one may wish to provide a. broader frame of reference to explain the behavior of agents who operate a. type or class of enterprises. By utilizing the analysis of the general economic theory of the firm one may introduce the additional constraints under which, for example, a public utility operates, and thereby derive a. theory of public utilities. Or, in the same way, one may wish to construct a, theory of transport firms, or a theory of retail firms, or a theory of manufacturing firms.