The central question of how adults learn has occupied the attention of scholars and practitioners since the founding of adult education as a professional field of practice in the 1920s. Some eighty years later, we have no single answer, no one theory or model of adult learning that explains all that we know about adult learners, the various contexts where learning takes place, and the process of learning itself. What we do have is a mosaic of theories, models, sets of principles, and explanations that, combined, compose the knowledge base of adult learning. Two7c important pieces of that mosaic are andragogy and self-directed learning. Other chapters in this volume focus on some of the newer approaches to understanding learning; the purpose of this chapter is to revisit two of the foundational theories of adult learning with an eye to assessing their" staving power" as important components of our present-day understanding of adult learning.