I. The increase in productivity with city size, 393. — II. The labor productivity of cities, 396. — III. The contributions of Hicks-neutral productivity and capital intensity, 401. — IV. The direction of causality, 406. — V. Conclusions, 410. — Appendix A: choice of the industries included in this study, 411. — Appendix B: evidence relating to the capital-labor ratio in cities of different size, 412.