Purpose: Despite the continuous growth of empirical studies exploring professional learning communities (PLCs) across different education systems, little is known about PLC instruments developed and used in existing research. This article aims to capture a full picture of existing PLC instruments developed since 1990. In so doing, the authors also pay attention to the seminal work of Karen Seashore Louis in alignment with the theme of the special issue. Design/methodology/approach: Based on the authors' searching databases, the authors identified eleven PLC instruments and 26 applied studies using the PLC instruments since 1990. Following this, the authors closely reviewed the identified studies and their relationships (i.e. which one influences which). Findings: The authors' review illuminates the measurement domains, conceptual origins and methodological soundness of the existing instruments and captures the impact of Louis's work on the applied studies using PLC instruments. Originality/value: Given that PLCs are seen as a policy measure to sustain and scale up school improvement internationally, the authors' review provides a better understanding of what and how researchers have measured the effect of PLCs on school improvement. As the first of its kind, the authors believe that their findings can give researchers valuable ideas about how to develop and use a PLC instrument.