NILDE is a document supply system and a library network used by more than 900 libraries, based on reciprocity. This article describes how this system works and how NILDE libraries cooperate to get reciprocal advantages. The paper also presents the example of Verona University Libraries, which participate in NILDE: the data show that through NILDE the ILL Service of Verona University Libraries can meet almost 90% of the document delivery requests of internal users, and almost all requests of external libraries. In conclusion, it is hoped that the experiences of reciprocity among libraries, even from different countries, can increase to ensure access to information for all users. In our opinion, this service also contributes to the achievement of the objectives of the UN 2030 Agenda for Sustainable Development.