The merits of user-driven design have long been acknowledged in the field of human–computer interaction (HCI): Closely involving target users throughout the lifecyle of a project can vastly improve their experiences with the final system. Thus, it comes as no surprise that a growing number of music technology researchers are beginning to incorporate user-driven techniques into their work, particularly as a means of evaluating their designs from the perspectives of their intended users. Many, however, have faced the limitations that arise from applying the task-based, quantitative techniques typically encountered in classical HCI research to the evaluation of nonutilitarian applications. The nature of musical performance requires that designers reevaluate their definitions of user “goals,” “tasks,” and “needs.” Furthermore, within the context of performance, the importance of creativity and enjoyment naturally supersedes that of efficiency, yet these concepts are more difficult to evaluate or quantify accurately. To address these challenges, this article contributes a set of key principles for the user-driven design and evaluation of novel interactive musical systems, along with a survey of evaluation techniques offered by new directions in HCI, ludology, interactive arts, and social-science research. Our goal is to help lay the foundation for designers of new musical interfaces to begin developing and customizing their own methodologies for measuring, in a concrete and systematic fashion, those critical aspects of the user experience that are often considered too nebulous for assessment.