Interconnectedness has been an important source of market failures, leading to the recent financial crisis. Large financial institutions tend to have similar exposures and thus exert externalities on each other through various mechanisms. Regulators have responded by putting more regulations in...

We develop a model in which asset commonality and short-term debt of banks interact to generate excessive systemic risk. Banks swap assets to diversify their individual risk. Two asset structures arise. In a clustered structure, groups of banks hold common asset portfolios and default together....