The present study is a contribution to the theory of the measurement of productivity growth. First, it examines the welfare-theoretic basis for measuring productivity growth and shows that the ideal welfare-theoretic measure is a chain index of productivity growth rates of different sectors which uses current output weights. Second, it lays out a technique for decomposing productivity growth which separates aggregate productivity growth into three factors — the pure productivity effect, the effect of changing shares, and the effect of different productivity levels. Finally, it shows how to apply the theoretically correct measure of productivity growth and indicates which of the three different components should be included in a welfare-oriented m...