This study examines factors that influence individual users' post-adoption switching behavior between information technology products that are near perfect substitutes. The introduction and popularity of Mozilla Firefox Web browser provided an ideal empirical setting for this study. Drawing upon literature on post-adoption user behavior, consumer behavior, and online user research, we propose a research model and validate it using cross-sectional field data collected from 306 users on their decision to switch from Microsoft Internet Explorer (IE) to Mozilla Firefox. Findings suggest that user satisfaction and breadth of use of the incumbent product are negatively associated with switching behavior. Perceived ease of use, relative advantage, and perceived security of the substitute product are positively associated with switching behavior. In addition, the effects of perceived ease of use and relative advantage are not moderated by user experience. This study contributes to both research and practice by advancing our understanding of information technology (IT) users' post-adoption behavior in general and their switching behavior on Web-related IT products specifically.