I argue that there exists a coherent and relevant tradition in economic thought that I label “price theory.” I define it as neoclassical microeconomic analysis that reduces rich and often incompletely specified models into “prices” (approximately) sufficient to characterize solutions to simple allocative problems. I illustrate this definition by highlighting distinctively price theoretic approaches to prominent research practices (diagrams and problems sets) and substantive research topics (e.g. selection markets and media slant). I trace the origins of price theory from the early nineteenth century through its segregation into the Chicago School in the last quarter of the twentieth. I argue that price theory plays a valuable complementary role to two traditions, “reductionism” and “empiricism,” with which I contrast it and show how this contribution of price theory has fueled a resurgence in this style of research in fields ranging from market design to international trade. Approximations critical to price theory are less formally developed than tools used in other methodological traditions, suggesting a research agenda to clarify the accuracy and range of validity of these methods.

I appreciate the clarification of my work by Tan and Wright, regret the confusing way my equations were labeled, and intended them to be interpreted in the manner they suggest is correct.

I develop a general theory of monopoly pricing of networks. Platforms use insulating tariffs to avoid coordination failure, implementing any desired allocation. Profit maximization distorts in the spirit of A. Michael Spence (1975) by internalizing only network externalities to marginal users. Thus the empirical and prescriptive content of the popular Jean-Charles Rochet and Jean Tirole (2006) model of two-sided markets turns on the nature of user heterogeneity. I propose a more plausible, yet equally tractable, model of heterogeneity in which users differ in their income or scale. My approach provides a general measure of market power and helps predict the effects of price regulation and mergers.

What is the best way to reward innovation? While prizes avoid deadweight loss, intellectual property (IP) selects high social surplus projects. Optimal innovation policy thus trades off the ex ante screening benefit and the ex post distortion. It solves a multidimensional screening problem in the private information held by the innovator: research cost, quality, and market size of the innovation. The appropriate degree of market power is never full monopoly pricing and is determined by measurable market characteristics, the inequality and elasticity of innovation supply, making the analysis open to empirical calibration. The framework has applications beyond IP policy to the optimal pricing of platforms or the optimal procurement of public infrastructure.

Calls for benefit-cost analysis in rule-making, based on the Dodd-Frank Wall Street Reform Act, have revealed a paucity of work on allocative efficiency in financial markets. We propose three principles to help fill this gap. First, we highlight the need for quantifying the statistical cost of a crisis to trade off the risk of a crisis against loss of growth during good times. Second, we propose a framework quantifying the social value of price discovery, and highlighting which arbitrages are over- and under-supplied from a social perspective. Finally, we distinguish between insurance benefits and gambling-facilitation harms of market completion.

Monopoly”. While many colleagues have provided valuable and in some cases detailed comments, special debts are due to Kevin Murphy (who originally inspired the work), Tony Atkinson and Faruk Gul (for suggesting the subtitle and title of the article, respectively), Luciano de Castro and Michael Salinger (for excellent formal conference discussions), Mark Armstrong, David Atkin and Dave Donaldson (for suggesting new results), Jesse Shapiro (for suggesting ways of reframing the paper) and above all Jeremy Bulow (for more things than can be listed here). Weyl is grateful

In selection markets, where the cost of serving consumers is heterogeneous and noncontractible, nonprice product features allow a firm to sort profitable from unprofitable consumers. An example of this “sorting by quality” is the use of down payments to dissuade borrowers who are unlikely to repay. We study a model in which consumers have multidimensional types and a firm offers a single product of endogenous quality, as in Spence (1975) . These two ingredients generate a novel sorting incentive in a firm’s first-order condition for quality, which is a simple ratio. The denominator is marginal consumer surplus, a measure of market power. The numerator is the covariance, among marginal consumers, between marginal willingness to pay for quality and cost to the firm. We provide conditions under which this term is signed and contrast the sorting incentives of a profit-maximizer and a social planner. We then use this characterization to quantify the importance of sorting empirically in subprime auto lending, analytically sign its impact in a model of add-on pricing, and calibrate optimal competition policy in health insurance markets.

Policies to correct market power and selection can be misguided when these forces coexist. We build a model of symmetric imperfect competition in selection markets that parameterizes the degree of market power and selection. We use graphical price-theoretic reasoning to characterize the interaction between these forces. Using a calibrated model of health insurance, we show that the risk adjustment commonly used to offset adverse selection can reduce coverage and social surplus. Conversely, in a calibrated model of subprime auto lending, realistic levels of competition can generate an oversupply of credit, implying that greater market power is desirable.

Holdout problems prevent private (voluntary and self-financing) assembly of complementary goods—such as land or dispersed spectrum—from many self-interested sellers. While mechanisms that fully respect sellers' property rights cannot alleviate these holdout problems, traditional solutions, such as the use of coercive government powers of “eminent domain” to expropriate property, can encourage wasteful and unfair assemblies. We discuss the problems holdout creates for the efficient operation of markets and how previous approaches have used regulated coercion to address these challenges. We then investigate when encouraging competition can partially or fully substitute for coercion, focusing particularly on questions of spectrum allocation.