Duality, Intermediate Inputs and Value-Added* *The original draft of this paper was written in 1971, partly supported by the Project for Quantitative Research in Economic Development at Harvard University. I am indebted to K.J. Arrow, Z. Griliches, R.E. Hall, L.J. Lau, and D. McFadden for helpful discussions. I am also grateful to M. Fuss who substantially revised the paper prior to its inclusion in the volume.