Credit institutions often refuse to lend money to small rms. Usually, this happens because small firms are not able to provide collateral to lenders. Moreover, given the small amount of required loans, the relative cost of full monitoring is too high for lenders. Group lending contracts have been viewed as an e ective solution to credit rationing of small rms in both developing and industrialized countries. e aim of this paper is to highlight the potential of group lending contracts in terms of credit risk management. In particular, this paper provides a theoretical explanation of the potential of group lending programs in screening good borrowers from bad ones to reduce the incidence of non-performing-loans (NPL). This paper shows that the success of firms involved in selected group lending programs is due to the fact that cosignature is an effective screening device: more precisely, if lenders make a proper use of co-signature to screen good firms from bad ones, then only firms that are good ex-ante enter group lending contracts. So, the main argument of this paper is that well designed group lending programs induce good rms to become jointly liable, at least partially, with other good firms and discourage other - bad - firms to do the same. Specifically, co-signature is proven to be a screening device only in the case of a perfectly competitive bank sector.