As search frictions in the market for a consumer product decline, buyers are able to locate and access more and more sellers. In response, sellers choose to design varieties of the product that are more and more specialized in order to take advantage of the heterogeneity in buyers' preferences. I find conditions on the fundamentals of the market under which the increase in specialization exactly offsets the decline in search frictions. Under these conditions, the extent of competition and the extent of price dispersion remain constant over time even though search frictions are vanishing. Buyer's surplus and seller's profit, however, grow over time at a constant endogenous rate, as the increase in specialization allows sellers to cater better and better to the preferences of individual buyers.

I derive a formula for the equilibrium distribution of markups in the search-theoretic model of imperfect competition of Butters (1977), Varian (1980), and Burdett andJudd (1983).The level of markups and the sign of the relationship between a seller's markup and its size depends on the extent of search frictions, as well as on other deep parameters.Markups are efficient.Markups are positive even though the varieties produced by sellers are perfect substitutes.Markups are heterogeneous even when all sellers operate the same production technology.Markups depend on size, even though the substitutability between a variety and the others does not depend on how much of that variety is consumed.Interpreting these markups through the lens of the monopolistic competition model of Dixit and Stiglitz (1977) would lead one to recover incorrect and unstable buyers' preferences.Interpreting these markups through the lens of the Dixit-Stiglitz model would also leads to incorrect policy recommendations.These results are a cautionary note on recent work in macroeconomics.

This article studies a search model of the labor market in which firms have private information about the quality of their vacancies, they can costlessly communicate with unemployed workers before the beginning of the application process, but the content of the communication does not constitute a contractual obligation. At the end of the application process, wages are determined as the outcome of an alternating offer bargaining game. The model is used to show that vague noncontractual announcements about compensation—such as those one is likely to find in help wanted ads—can be correlated with actual wages and can partially direct the search strategy of workers.

For a search-theoretic model of the labor market, we seek conditions for the existence of a balanced growth path (BGP), where unemployment, vacancy, and worker’s transitions rates remain constant in the face of improvements in the production and search technologies. A BGP exists iff firm-worker matches are inspection goods and the quality of a match is drawn from a Pareto distribution. Declining search frictions contribute to growth with an intensity determined by the tail coefficient of the Pareto distribution. We develop a strategy to measure the rate of decline of search frictions and their contribution to growth.

We propose a theory of self-fulfilling unemployment fluctuations. When a firm increases its workforce, it raises demand and weakens competition facing other firms, as employed workers spend more and have less time to search for low prices than unemployed workers. These effects induce other firms to hire more labor in order to scale up their presence in the product market. The feedback between employment and product market conditions generates multiple equilibria—and the possibility of self-fulfilling fluctuations—if differences in shopping behavior between employed and unemployed are large enough. Evidence on spending, shopping, and prices suggests that this is the case.

We study two wage bargaining games between a firm and multiple workers. We revisit the bargaining game proposed by Stole and Zwiebel. We show that, in the unique Subgame Perfect Equilibrium, the gains from trade captured by workers who bargain earlier with the firm are larger than those captured by workers who bargain later, as well as larger than those captured by the firm. The resulting equilibrium payoffs are different from those reported in Stole and Zwiebel as they are not the Shapley values. We propose a novel bargaining game, the Rolodex game, which follows a simple and realistic protocol. In the unique no-delay Subgame Perfect Equilibrium of this game, the payoffs to the firm and to the workers are their Shapley values.

To what extent is a worker's human capital growth affected by the quality of his coworkers? To answer this question, we develop and estimate a model in which the productivity and the human capital growth of an individual depend on the average human capital of his coworkers. The measured production function is supermodular: The marginal product of a more knowledgeable individual is increasing in the human capital of his coworkers. The measured human capital accumulation function is convex: An individual's human capital growth is increasing in coworkers' human capital only when paired with more knowledgeable coworkers, but independent of coworkers' human capital when paired with less knowledgeable coworkers. Learning from coworkers accounts for two thirds of the stock of human capital accumulated on the job. Technological changes that increase production supermodularity lead to labor market segregation and, by reducing the opportunities for low human capital workers to learn from better coworkers, lead to a decline in aggregate human capital and output.