This paper develops a model of repeated innovation with knowledge spillovers. The model's novel feature is that firms compete on two dimensions: (1) product quality, where one firm's innovation ultimately spills over to other firms; and (2) distribution costs, where there are no spillovers across firms and where learning-by-doing on the part of incumbent firms gives them a competitive advantage over would-be entrants. Such firm-specific learning-by-doing has two important consequences: (1) it can in some circumstances dramatically reduce the long-run average level of innovation; (2) it leads to endogeneous bunching, or waves, in innovative activity.

This paper examines the “term structure” of options' implied volatilities, using data on S&P 100 index options. Because implied volatility is strongly mean reverting, the implied volatility on a longer maturity option should move by less than one percent in response to a one percent move in the implied volatility of a shorter maturity option. Empirically, this elasticity turns out to be larger than suggested by rational expectations theory—long-maturity options tend to “overreact” to changes in the implied volatility of short-maturity options.

This paper examines the “term structure” of options' implied volatilities, using data on S&P 100 index options. Because implied volatility is strongly mean reverting, the implied volatility on a longer maturity option should move by less than one percent in response to a one percent move in the implied volatility of a shorter maturity option. Empirically, this elasticity turns out to be larger than suggested by rational expectations theory—long‐maturity options tend to “overreact” to changes in the implied volatility of short‐maturity options.

The majority of asset-management intermediaries (e.g., mutual funds, hedge funds) are structured on an open-end basis, even though it appears that the open-end form can be a serious impediment to arbitrage. I argue that the equilibrium degree of open-ending in an economy can be excessive from the point of view of investors. When funds compete for investors' dollars, they may engage in a counterproductive race towards the open-end form, even though this form leaves them ill-suited to undertaking certain types of arbitrage trades. One implication of the analysis is that, even absent short-sales constraints or other frictions, economically large mispricings can coexist with rational, competitive arbitrageurs who earn small excess returns.

This paper develops a model of inefficient managerial behavior in the face of a rational stock market In an effort to mislead the market about their firms' worth, managers forsake good investments so as to boost current earnings. In equilibrium the market is efficient and is not fooled: it correctly conjectures that there will be earnings inflation, and adjusts for this in making inferences. Nonetheless, managers, who take the market's conjectures as fixed, continue to behave myopically. The model is useful in assessing evidence that has been presented in che “myopia” debate. It also yields some novel implications regarding firm structure and the limits of intergation.

I develop a model of bilateral conversations in which players honestly exchange ideas with their competitors. The key to incentive compatibility is complementarity in the information structure: a player can generate a new insight only if he has access to his counterpart's previous thoughts on a topic. I then examine a social network in which A has a conversation with B, then B has a conversation with C, and so on. Relatively underdeveloped ideas can travel long distances over the network. More valuable ideas, by contrast, tend to remain localized among small groups of agents.

This paper examines the problem faced by the Federal Reserve in announcing its private information about its future policies. Because it would like to manipulate expectations and pursue a time-inconsistent policy, the Fed cannot reveal its policy objectives precisely and credibly. It can, however, communicate some information about its goals through the cheap talk mechanism of Vincent Crawford and Joel Sobel: making announcements that are imprecise, and only giving ranges within which these goals may lie.

Stock‐market trading is increasingly dominated by sophisticated professionals, as opposed to individual investors. Will this trend ultimately lead to greater market efficiency? I consider two complicating factors. The first is crowding—the fact that, for a wide range of “unanchored” strategies, an arbitrageur cannot know how many of his peers are simultaneously entering the same trade. The second is leverage—when an arbitrageur chooses a privately optimal leverage ratio, he may create a fire‐sale externality that raises the likelihood of a severe crash. In some cases, capital regulation may be helpful in dealing with the latter problem.