I am pleased to write a commentary on this excellent chapter on Third Sector research. While nonprofit or Third Sector research has a history of more than half a century, until the 1980s, it focused primarily on nonprofit organizations and philanthropy in the United States. Since the 1990s, however, the Johns Hopkins Comparative Nonprofit Sector Project (CNP) has been launched, and the question has been raised as to whether research on U.S. nonprofits is equally applicable to the nonprofit sector outside the U.S. In this chapter, Stefan Toepler and Helmut K. Anheier, who have led CNP, address the definition, classification, and causes of international differences in the nonprofit sector based on the research findings of the CNP. They also suggest a set of research agendas for next-generation scholars. Based on my experience as one of the country experts of CNP, I would like to examine critically (1) how to define and explain the cross-national difference in the Third Sector and (2) how to build sustainable core data infrastructure.