From its foundation in 1980, the ISTC has been one of the most important international reference sources for incunabula studies. Based on a merger of F.R. Goff’s Incunabula in North American Libraries: A Third Census and the Indice Generale degli Incunaboli delle Biblioteche d’Italia, it aimed to be a comprehensive list both of 15th-century editions and of surviving copies of incunabula. While maintaining its original purpose, it has striven to take advantage of new partnerships and technical innovations to ensure its continued utility as a cornerstone of incunabula research. Managed by the British Library in London and hosted by CERL, the ISTC continues to rely on cooperation and partnership from holding institutions and researchers worldwide. Free since 2003, the ISTC can be used as a simple guide to editions and copies, but also as a dataset enabling researchers to look at 15th-century printing in new ways. After briefly looking at the ISTC’s history, this essay focuses on new developments made to the database, highlighting its continued relevance and potential to support traditional incunabula research as well as new projects, and its managers’ intention and flexibility to improve the file in response to its users’ feedback.