This book brings together in a single coherent framework a research programme begun by the author in the forties. The main model around which the analysis is built is Hicksian in character, having been drawn in large part from John Hicks's Value and Capital. The model is extended so as to include money and securities. In respect of the theory of the firm the model focuses on demand and supply plans, on inputs and outputs, on inventories, and on dependencies between them. The stability of temporary equilibrium is discussed for linear and non-linear cases. Because the concept of structural stability is important for understanding non-linear cases, it is defined and applied to the case of economic motion generated from the temporary equilibrium analysis. The addenda focus on developments in economic theory following the publication of the main model.