After the Italian third sector reform, third sector organizations and social enterpris-es have to cope with the accountability principle more than ever. They also need to find new strategies to report their results to their stakeholders and communities. The most critical issue that this article wants to tackle is to find a methodology for social impact accounting that is flexible, viable for organizations with very differ-ent characteristics (e.g. sector of intervention, dimension, legal forms, etc.), and scientifically robust. This article aims to identify a social impact accounting meth-odology that every third sector organization and social enterprise could implement. After the introduction and the literature review, the article presents a proposal for a social impact accounting model and case studies from a social enterprise and two third sector organizations in Tuscany. The last part of the article presents the final remarks and some suggestions for further research as, for example, the develop-ment of a public database of proxies to be used to provide a financial quantifica-tion for the social outcomes achieved by third sector organizations and social en-terprises.
Keywords: Impatto sociale, terzo settore, accountability, SROI, valutazione, sta-keholder engagement