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The high-tech sector is concentrated in a small number of cities. The ten largest clusters in computer science, semiconductors, and biology account for 69 percent, 77 percent, and 59 percent of all US inventors, respectively. Using longitudinal data on 109,846 inventors, I find that geographical agglomeration results in significant productivity gains. When an inventor moves to a city with a large cluster of inventors in the same field, she experiences a sizable increase in the number and quality of patents produced. The presence of significant productivity externalities implies that the agglomeration of inventors generates large gains in the aggregate amount of innovation produced in the United States.

How do geographically concentrated income shocks influence the long-run spatial distribution of poverty within a city? We examine the impact on housing prices of a cholera epidemic in one neighborhood of nineteenth century London. Ten years after the epidemic, housing prices are significantly lower just inside the catchment area of the water pump that transmitted the disease. Moreover, differences in housing prices persist over the following 160 years. We make sense of these patterns by building a model of a rental market with frictions in which poor tenants exert a negative externality on their neighbors. This showcases how a locally concentrated income shock can persistently change the tenant composition of a block.

This paper develops a theory of optimal taxation with behavioral agents. We use a general framework that encompasses a wide range of biases such as misperceptions and internalities. We revisit the three pillars of optimal taxation: Ramsey (linear commodity taxation to raise revenues and redistribute), Pigou (linear commodity taxation to correct externalities), and Mirrlees (nonlinear income taxation). We show how the canonical optimal tax formulas are modified and lead to novel economic insights. We also show how to incorporate nudges in the optimal taxation framework, and jointly characterize optimal taxes and nudges.

We study games in which a network mediates strategic spillovers and externalities among the players. How does a planner optimally target interventions that change individuals’ private returns to investment? We analyze this question by decomposing any intervention into orthogonal principal components, which are determined by the network and are ordered according to their associated eigenvalues. There is a close connection between the nature of spillovers and the representation of various principal components in the optimal intervention. In games of strategic complements (substitutes), interventions place more weight on the top (bottom) principal components, which reflect more global (local) network structure. For large budgets, optimal interventions are simple—they essentially involve only a single principal component.

Intellectual property (IP) can internalize positive externalities associated with the creation and discovery of ideas, thereby increasing investment in efforts to create and discover ideas. However, IP law also causes negative externalities. Strict IP rights raise the transaction costs associated with consuming and building on existing ideas. This causes a tragedy of the anticommons, in which valuable resources are underused and underdeveloped. By disincentivizing creative projects that build on existing ideas, IP protection, even if it increases original innovation, can inadvertently reduce the rate of iterative innovation. The net effect of IP law on innovation and welfare depends on the relative magnitude of these positive and negative externalities. We argue that the current regime probably suffers from excessive, and excessively rigid, IP protection. This motivates the search for institutional alternatives and complements. We suggest that a monocentric IP rights regime may not be the only, or the most efficient, way to internalize the positive externalities of innovation. The knowledge economy supports the emergence of diverse, polycentric forms of bottom-up self-governance, both market and community led, that entail the citizen coproduction of the norms and practices of intellectual creation and discovery.

This survey investigates the increasing importance of global public goods (GPGs) in today’s interdependent world, driven by ever-growing, cross-border externalities and public good spillovers. Novel technologies, enhanced globalization, and population increases are among the main drivers of the rise of GPGs. Key GPGs include curbing climate change, instituting universal regulatory practices, eradicating infectious diseases, preserving world peace, discovering scientific breakthroughs, and limiting financial crises. The survey presents a compact theoretical foundation for GPGs, grounded in the provision of public goods. Because countries may be contributors or noncontributors to a particular GPG, coalition formation and behavior play a role, as do strategic interactions between a contributor coalition and other countries. In the survey, recurrent themes include strategic considerations, alternative institutional arrangements, GPGs’ defining properties, new actors’ roles, and collective action concerns. The four properties of GPGs—benefit non-rivalry, benefit non-excludability, aggregator technology, and spillover range—influence the GPGs’ supply prognoses and the need for and form of provision intervention, which may affect the requisite institutional changes. Three representative case studies illustrate how theoretical insights inform policy and empirical tests. Regional public goods are shown to involve a question of subsidiarity and different actors compared to GPGs.

We combine a theoretical discrete-choice model of vehicle purchases, an econometric analysis of electricity emissions, and the AP2 air pollution model to estimate the geographic variation in the environmental benefits from driving electric vehicles. The second-best electric vehicle purchase subsidy ranges from $2,785 in California to —$4,964 in North Dakota, with a mean of —$1,095. Ninety percent of local environmental externalities from driving electric vehicles in one state are exported to others, implying they may be subsidized locally, even when the environmental benefits are negative overall. Geographically differentiated subsidies can reduce deadweight loss, but only modestly.

Although externality is one of the basic concepts in economics, its rigorous definition remains elusive. This paper reconceptualizes externality as an instance of a broader phenomenon of incompatibility of plans—a situation where plans of different individuals cannot be materialized simultaneously because they compete for resources that are scarce. The plan incompatibility can be addressed by institutional arrangements involving mechanisms that determine which plans will be realized. Various institutional arrangements can be compared from the perspective of efficiency, operational costs, distributional effects, and other criteria. Regardless of the institutional arrangement, the spillover effects are unavoidable, as they are implied by scarcity. Therefore, the analysis of externalities should shift its focus from spillover effects to the mechanisms for allocating scarce resources among competing plans.

In a product market where consumers are open to uninformed purchases, we study competition between a traditional and an online retailer in the presence of showrooming. Several results are obtained. First, showrooming intensifies competition and lowers both firms’ profits, thus supporting traditional and online retailers’ recent strategy of carrying more exclusive varieties. Second, lowering consumer search costs may aggravate showrooming and decrease the traditional retailer’s profits for intermediate search costs. Third, opening an online store expands the demand of the traditional retailer but intensifies competition, thus lowering its profits under certain conditions. Fourth, a return policy by the online retailer alleviates showrooming and relaxes competition but weakly reduces its demand, increasing its profits only for intermediate search costs. The return policy (weakly) increases the traditional retailer’s profits. Fifth, when search cost is not high enough, price matching by the traditional retailer may also intensify competition and hurt its profits. We then examine how webrooming interacts with showrooming. When webrooming resolves partial match uncertainty, it may increase both firms’ profits by inducing more consumers to participate. The online appendix is available at https://doi.org/10.1287/mksc.2018.1084 .

When a user shares her data with online platforms, she reveals information about others. In such a setting, externalities depress the price of data because once a user's information is leaked by others, she has less reason to protect her data and privacy. These depressed prices lead to excessive data sharing. We characterize conditions under which shutting down data markets improves welfare. Platform competition does not redress the problem of excessively low data prices and too much data sharing and may further reduce welfare. We propose a scheme based on mediated data sharing that improves efficiency.