ABSTRACT: It is recognized that change management is necessary for information technology implementation success. While there are a growing number of interorganizational systems (IOS) designed for the public, there is little study of and lack of clear guidelines on managing change related to their implementation. This research explores the phenomenon through the case study of a country-wide farecard system implemented in Singapore's public transportation system that involved several organizations and the public. Through the case analysis, we identified critical success factors (CSFs) for change management in IOS for the public and interrelated them using a causal loop diagram (CLD). These factors included refinements of existing CSFs identified from the literature as well as new CSFs from our case study. Our case analysis showed that communication through senior management and cooperation of affected organizations in the system implementation was able to overcome resistance to change in these organizations. We also found that while comprehensive publicity could initiate change in the public, a critical mass had to be built up for managing public change by coopting public opinion leaders as well. By interrelating CSFs identified in the case via a CLD, this study provides a preliminary theoretical framework for studying change management in IOS for the public and aims to guide practitioners in implementing such systems.