Introduction 2. Definitions and Notation 3. Profit Maximizing Expansion Paths 4. A Simple Example of an Expansion Path 5. Conditions for Economies of Scale to be Observed 6. General Solution for Two Products 7. Two Input Factors 8. Some Applications 9. Conclusions Appendix A. Economies of Scale in Income versus Costs Appendix B. Slope of the Production Possibility Isoquants and the Income Isoquants References