Self-assessment is paired with continuing medical education in the "lifelong learning " component of the American Board of Radiology's (ABR) Maintenance of Certification program. The literature on the use of self-assessment in higher education and the professions is instructive with regard to the distinctiveness of this form of adult learning. This article reviews pertinent literature, summarizes the findings, and applies the principles to the creation and use of "self-assessment modules" (SAMs) for the maintenance of certification. Data on the use of ABR-qualified SAMs are reported. On completion of this article, the reader should be able to describe the nature, role, and best practices of self-assessment; apply these concepts to the creation or use of a SAM; and identify future opportunities for SAM development and use that will enhance the lifelong learning of radiologists.