Maintenance of posture and locomotion are, to varying degrees, critical components of all land-based exercise and athletic activities. The biomechanics and physiology of posture and locomotion have been among the most extensively studied of human activities. This chapter (a) introduces the exercise professional to biomechanical and physiological issues associated with postural control and gait and (b) provides a basis for understanding the experimental methods used to make quantitative biomechanical and physiological measurements associated with postural control and gait, the outcome variables, the interpretation of the variables, and the limitations of the interpretations. The reference list provides sources through which detailed treatment of many of the concepts may be explored. the first part of this chapter presents a framework of biomechanical fundamentals as they relate to the biomechanics of postural control and postural stability. The second part of this chapter presents some of the basic relationships between the biomechanics and physiology of gait, specifically as they relate to the topic of economy.