The paper has two parts. The first one contains a description of the development of the SEMTSA approach since the early 1970s, its applications to macroeconomic variables, the rationalisation of applied models using economic theory, and the extension to disaggregated models within the framework of Marshallian competitive models for production sectors. The second part is devoted to the theoretical derivation of different formulations of the Marshallian macroeconomic model with increasing complexity, starting with a one-sector model with supply, demand, and entry/exit equations, and continuing with models in the single-sector case but extended to demand and supply factor equations to end up with n-sector models, which are closed by the inclusion of government and money equations. In this part of the paper, the initial structural models are in differential equation form, leading to reduced form equations useful for forecasting purposes and discrete approximation proposals. In this process, the convergence properties of the main endogenous variables of the differential and difference equation models are illustrated for different values of the parameters and for given initial conditions. It is shown that the difference equation model can approach equilibrium values with oscillatory behaviour and that a wide range of solutions is possible. All this reveals the potential of this theoretical framework for structural analysis, forecasting, and policy simulation in applied macroeconomics.Professor Zellner is one of the most outstanding econometricians since the late 1950s, when he published his initial contributions on the consumption function. He has been a highly productive scholar in many fields, such as statistics, econometric theory, methodology, applied econometrics, etc. His research, no matter how theoretical and technical, is always conducted with the aim of producing results which could be used to obtain a better understanding of the real world, and this is why Professor Zellner's research has had such a broad and deep impact on modern econometrics. Today's paper is a very good example of this and is, in fact, highly significant for macroeconometrics. It explains the orientation linking the research in a long sequence of previous papers by the author with a number of important collaborators since the first famous Zellner and Palm paper was published in 1974. These results show that the strategy of developing appropriate and rigorous statisticaleconometric tools for building econometric models using a basic economic theory, which are then fitted to data to test how well they perform and to learn how they can be improved, has been very successful. This 0169-2070/$ -see front matter D