Before revision:  We give conditions under which the equilibrium network is driven to a fragile configuration, where arbitrarily small aggregate shocks cause discontinuous losses. We use the model to provide a unified account of a number of stylized facts about complex economies .
After revision:  We give conditions under which the equilibrium network is driven to a fragile configuration, where arbitrarily small aggregate shocks to relationships causing arbitrarily steep drops in output. The endogenous configuration of supply networks provides a new channel for the powerful amplification of shocks .