I. Introduction -- 1.1 Scope and significance -- 1.2 Methodological considerations -- 1.3 An outline of the remaining chapters -- II. Some elements from the neoclassical research programme of the firm -- 2.1 Introduction -- 2.2 Keynesian theories of the firm -- 2.3 The neoclassical programme -- 2.4 An outline of the structure of the models of this study -- III. A neoclassical model of a firm subject to a putty-putty technology -- 3.1 The market- and information structure -- 3.2 The production structure -- 3.3 The full model -- 3.4 Existence of an optimal policy -- 3.5 Necessary conditions for an optimal policy -- 3.6 Approximate solutions -- 3.7 Comparison with the stock adjustment specification -- IV. Vintage technologies and the theory of the firm -- 4.1 Introduction -- 4.2 The structure of putty-clay models -- 4.3 A general putty-clay model -- V Estimation and empirical testing of the putty-putty model -- 5.1 Discrete-time adaptions -- 5.2 The construction of the expectations -- 5.3 Estimation -- 5.4 Model specification tests -- 5.5 Model characteristics -- 5.6 Trends and fluctuations -- VI. Estimation and testing of the putty-clay model -- 6.1 Discrete-time adaptions -- 6.2 Estimation -- 6.3 Model specification tests -- 6.4 Model characteristics -- 6.4.1 Stochastic stability -- 6.5 Trends and fluctuations -- VII. Summary and conclusion -- 7.1 Summary -- 7.2 Conclusion -- List of symbols -- References -- Author index.