A model is presented to help clarify the concept of lifelong learning. Constructed on the idea that an operational definition of lifelong learning should be based on the locus of control for making decisions about the goals and means of learning, the model is a two-by-two matrix of learner and institution that represents four identified situations of learning: formal (learners have little control over the objectives or means of learning); nonformal (learners control the objectives but not the means of learning); informal (learners control the means but not the objectives of learning); and self-directed (learners control both the objectives and means of learning). The model is interpreted as demonstrating how all planned or deliberate learning is located along a continuum; the concept of control provides the basis for classifying the various types of lifelong learning. From the model the authors also suggest that lifelong learning is neither the domain of a particular age group nor a single program or piece of legislation; it is a composite of many programs, pieces of legislation, and learner-initiated activities. To further clarify the model, expansions (based on research) of formal, nonformal, and informal learning are provided. Then, using the established model, an in-depth examination is made of the ultimate state of learner autonomy: self-directed learning. Included in the discussion is a review of previous research and a look at current research and trends. A list of references concludes the paper. (CT)