What is the role of startups within the innovation ecosystem? Since 2000, startups have grown in their share of commercializing research from top U.S. universities; however, prior work has little to say on the particular advantages of startup ventures in the innovation process relative to more...

This handbook chapter studies the theoretical micro-foundations of urban agglomeration economies. We distinguish three types of micro-foundations, based on sharing, matching, and learning mechanisms. For each of these three categories, we develop one or more core models in detail and discuss the...

When economic activity is concentrated over space or over time, it is more efficient. Most production occurs in geographic hot spots, and most production occurs between 9 and 12 in the morning and 1 to 5 in the afternoon on weekdays. The thick-market efficiencies that encourage the concentration...

This review discusses frontier topics in economic geography as they relate to firms and agglomeration economies. We focus on areas where empirical research is scarce but possible. We first outline a conceptual framework for city formation that allows us to contemplate what empiricists might...

This paper studies the sources of agglomeration economies in cities. We begin by introducing a simple dynamic spatial equilibrium model that incorporates spillovers within and across industries, as well as city-size effects. The model generates a dynamic panel-data estimation equation. We...

In many cities, restaurants and retail establishments are spatially concentrated. Economists have long recognized the presence of demand externalities that arise from spatial agglomeration as a possible explanation, but empirically identifying this type of spillovers has proven difficult. We...

We document a novel stylized fact: Using data for several countries, we show that export activity is disproportionately concentrated in larger cities - even more so than overall economic activity. We account for this fact by marrying elements of international trade and economic geography. We...

There is a strong connection between per worker productivity and metropolitan area population, which is commonly interpreted as evidence for the existence of agglomeration economies. This correlation is particularly strong in cities with higher levels of skill and virtually non-existent in less...