Identifying the critical success factors (CSFs) of institutional repositories can influence their successful implementation. This study investigates the perceived importance of the success factors and the actual performance of institutional repositories worldwide. A web-based questionnaire was distributed to 354 repository managers via the OpenDOAR email distribution service and achieved a response rate of 83.3%. Factor analysis indicated the possibility of 46 variables under six factors being important for the success of institutional repository implementation. The six factors are Management, Services, Technology, Self-archive practices, People, and Resources. A gap analysis was conducted to identify the importance and actual performance of the factors. The major finding was that several of the factors are not fully realised by the institutional repositories despite their relative importance. Institutional repositories are still in development; this study may help to guide their implementation and further development.