This paper explores the roles of explicit and tacit knowledge in performance improvement as experience is gained with a new technology. We propose that the same technology can present simultaneous opportunities for improvement along distinct performance dimensions, such as efficiency and breadth of use. Drawing from research on new technology implementation and knowledge management, we develop a framework relating type of user of a new technology (individual or group) to type of knowledge (tacit or explicit) to suggest implications for performance improvement curves. Past research has investigated knowledge and transfer problems for individuals; in contrast, this paper proposes differences in patterns of performance improvement for groups using a new technology as a function of the type of knowledge involved in each dimension of performance. To explore these propositions, we analyze data from 311 surgical procedures at 15 hospitals learning to use a new cardiac surgery technology.