Few studies in technology acceptance have explicitly addressed the acceptance of replacement technologies, technologies that replace legacy ones that have been in use. This article explores this issue through the theoretical lens of mental models. We contend that accepting replacement technologies entails both mental model maintenance and mental model building: mental model maintenance enables users to apply their knowledge of the legacy technologies, and mental model building helps users acquire new knowledge and reform their understanding to use replacement technologies. Both processes affect user perceptions about replacement technologies, which in turn affect user intentions to use them. In addition, this study explores how perceived compatibility between replacement and legacy technologies affects both mental model processes. A research model was developed and empirically tested with survey data. The results in general support our arguments. Based on the findings, we offer a few suggestions that can promote user acceptance of replacement technologies. (Contains 3 tables and 2 figures.)