Physical activity is essential for bone health. The most compelling evidence for this is the rapid and profound bone loss that occurs during conditions of extreme physical inactivity (e.g., bed rest, limb immobilization). However, the optimal exercise prescription to increase or maintain bone mass and strength in adults remains uncertain. This lecture will discuss which components of an exercise program (i.e., mode, intensity, frequency, duration) are important for stimulating an anabolic response in bone, and will also present emerging evidence that exercise can invoke a potent catabolic skeletal response.