This special issue is focused on investigating the role of learners’ self-identification with disciplinary endeavors (e.g., science-related investigations, interpretations of historical events) in relation to the design of and their participation in learning environments. Over the past decade there has been a growing body of research focused on how learners’ ideas about themselves as social actors in activities mediate participation within and across learning environments and how the development of learners’ disciplinary identities can be a productive goal of educational interventions. In this work, the disciplinary identities of learners help explain how and why individuals engage within and across the learning environments they frequent. They also provide a window onto how learners and their compatriots locate and leverage resources for the ongoing pursuit of subject matter learning—in which youth attempt to engage in ongoing learning. It is important to note that this theoretical lens highlights how learning environments always have implicit or explicit goals with respect to disciplinary identification—and how learners take up, resist, transform, or are marginalized by those goals.