This study reviews empirical research on inter-organizational trust. Since the early 1990s, researchers on inter-organizational relationships have consistently argued that mutual trust is an essential factor of relationship quality and performance. The purpose of the study was to evaluate the advancements and setbacks in current empirical research in terms of measuring inter-organizational trust. This paper analyzes the theoretical approach, the conceptualization and operationalization, and the measurement issues covered in studies on inter-organizational trust conducted from 1990 to 2003. Although trust has emerged as an important factor in inter-organizational relationships, there are still major conceptual and methodological challenges to be met in studying this complex concept. The results show major inconsistencies in conceptualization, operationalization, and measurement of trust. The paper concludes with suggestions for further empirical research.