This study explores the implementation of a largescale online extensive reading program (ERP) at a university in Thailand. The program was integrated into two English foundation courses in one academic year and consisted of over 5,000 freshmen and 60 teachers. In-depth interviews were conducted with three administrators who were decision-makers, one ERP coordinator, and 10 classroom teachers. The results reveal that these stakeholders played their parts in making the ERP implementation successful. Also, five factors in successful ERPs, including the integration of extensive reading into the curriculum, the availability of reading materials, the institution-level support, teacher's roles, and the use of an online platform were present in this ERP. Suggestions to newcomers who plan to implement an ERP are also provided.