Is there excessive trading volume in financial markets? Recent proposals to tax transactions, limit short selling, or restrict clienteles for particular financial products reflect such a view but beg the fundamental question of how much trading is optimal for an economy. We show that the optimal...

Market behavior is the central topic of economics. Yet while economists have a good understanding of the behavior of well-functioning markets, we have little to say about market fragility, market resiliency, and market collapse. Research emerging at the frontier between computer science and...

A goal for stock exchanges is to increase participation by firms and investors. We show how specific features of the microstructure can reduce perceived ambiguity, and induce participation by both investors and issuers. We develop a model with sophisticated traders, who we view as expected...

In the current credit crisis there is little or no trade in a variety of financial assets, even though bids and asks exist for many of these assets. We develop a model in which this illiquidity arises from uncertainty, and we argue that this new form of illiquidity makes bid and ask prices...