This paper describes some of the key research works related to my PhD thesis. The goal is the development of a global approach to digital library (DL) evaluation towards quality interoperability. DL evaluation has a vital role to play in building DLs, and in understanding and enhancing their role in society. Responding to two parallel research needs, the project is grouped around two tracks. Track one covers the theoretical approach, and provides an integrated evaluation model which overcomes the fragmentation of quality assessments; track two covers the experimental side, which has been undertaken through a comparative analysis of different DL evaluation methodologies, relating them to the conceptual framework. After presenting the problem dentition, current background and related work, this paper enumerates a set of research questions and hypotheses that I would like to address, and outlines the research methodology, focusing on a proposed evaluation framework and on the lessons learned from the case studies
