Wang, XY2016-12-062015-02-23https://hdl.handle.net/10161/13171Heterogeneously risk-averse individuals who lack access to formal insurance build and use relationships with each other to manage risk. I show that the composition of equilibrium relationships under pairwise matching and when group size is endogenous is determined by a mean-variance trade-off across differentially risky productive opportunities, though output distributions may have infinitely-many nonzero cumulants. This has important policy implications. For example, a policy which ignores the equilibrium response of informal institutions may exacerbate inequality and hurt most those it intended to help: a reduction in aggregate risk may lead to an increase in risk borne by the most risk-averse individuals, as the least risk-averse abandon their roles as informal insurers. The theory also sheds light on the channels through which endogenous insurance relationships influence informal firm structure and entrepreneurship.assortative matchingrisk sharinginformal insuranceformal insurancegroup formationJournal article