Part 1 †This survey is the outgrowth of lectures we gave at the Institute for Mathematical Studies in the Social Sciences (IMSSS), Stanford University, in the summer of 1983. Our research was supported by National Science Foundation grants SES 81–04769 and SES 82–01373 at the IMSSS, and by SES 82–07925 at the University of California, Berkeley. The authors would like to thank John Geanakoplos, David Kreps, Eric Maskin, John Roberts, Jose Scheinkman and Robert Wilson for helpful conversations, and Mordecai Kurz for encouraging us to undertake this project., Drew Fudenberg, Jean Tirole; Chapter 1 Introduction; Chapter 2 Competition in Tangible Variables; Chapter 3 Preemption; Chapter 4 Short-Run Commitment, Fixed Costs, and Natural Monopolies; Chapter 5 Price Wars and Tacit Collusion; Chapter 6 Investing in Disinformation;