Sport psychologists know that many people who do a behavior voluntarily over a long period of time have discovered for themselves an inner feeling that motivates them to perform the behavior, such as exercise, for its own sake. This form of motivation has been labeled "intrinsic" by some researchers. The concept of intrinsic motivation, when applied to physical activity, focuses on helping people develop a mindset that elicits enjoyment and fun from the experience itself. The experience then becomes a more powerful one, strong enough to draw the person back time and time again. What this approach suggests is that cultivating the experience of the intrinsic exerciser is essential for sustainable change, whether in children, young adults, middle-age adults, or older adults. The concept of intrinsic motivation is especially important when helping young adults, because they are continuously bombarded by external stimuli and are at a high risk for losing touch with the joy of movement simply because they lack attention skills. Without the experience of fun or enjoyment, behavior change will not be sustained because performing the behavior becomes drudgery. In the author's view, four psychological concepts--vision, mastery, flow, and inergy--can help people of any age become more intrinsic with their physical activity, thereby increasing enjoyment and motivating a more regular exercise routine (Kimiecik, 2002). This article provides an overview of each of these intrinsic ideas and how together they provide opportunities for optimal physical activity experiences that can be sustained throughout life.