Over the past forty years, Howard Barrows' contributions to PBL research have influenced and guided educational research and practice in a diversity of domains. It is necessary to make visible to all PBL scholars what has been accomplished, what is perceived as significant, and what is the scope of applicability for Barrows' groundbreaking findings. As more disciplines recognize Barrows' efforts and adopt PBL in education, it becomes crucial but challenging to sustain community memory so that PBL scholars are kept well informed of research innovations in various domains. In this paper, we review Barrows' scholarly efforts in PBL and reveal the impacts on subsequent studies in various domains. A bibliometrics analysis is conducted on Barrows' PBL publications and the corresponding citations to quantitatively measure Barrows' impact. Our findings demonstrate Barrows' exceptional contributions to PBL and the disciplinary differences in conducting PBL studies based on Barrows' work. It is also revealed that PBL scholars who share similar interests have rarely collaborated with each other. The PBL research community has a real opportunity to connect isolated research groups and reduce the fragmentation so that research innovations in one domain can be disseminated to inform other scholars.