Who were the people at the cutting edge of social reform in Europe between 1840 and 1880, and how were they connected? This article proposes a method to locate a transnational community of experts involved in social reform and focuses on the ways in which these experts shared and spread their knowledge across borders. After a discussion of the concepts of social reform, transnationalization, and transfer, we show how we built a database of visitors to social reform congresses in the period 1840-1880, and explain how we extracted a core group of experts from this database. This "congress elite'' is the focus of the second part of this article, in which we discuss their travels, congress visits, publications, correspondence, and membership of learned and professional organizations. We argue that individual members of our elite, leaning on the prestige of their international contacts, shaped reform debates in their home countries. We conclude by calling for further research into the influence that the transnational elite were able to exert on concrete social reforms in different national frameworks in order to assess to what extent they can be regarded as an "epistemic community in the making''.