In this paper we explore contagion from one institution to another that can stem from the existence of a network of financial contracts. Informational con- tagion, as a second possible form of systemic risk, has been also considered. The intricate web of claims and obligations linking the balance sheets of financial institutions and consumers’ behavior have been modeled in a structure that reflects the complexities of observed financial networks and the diffusion of crisis expectations. The agent based model we propose provides a suitable microeconomic framework for analyzing the relation between the structure of a financial network, i.e. the size and the pattern of obligations, and its exposure to systemic risk.