How do humans maintain their balance? This question may sound silly since maintaining balance is one of the easiest and the most fundamental tasks that humans could ever achieve in the history. However, being more prudent, we may understand that maintaining balance is complicated processes of neural and musculoskeletal actions or sensorimotor integration at the brain, various pathways, and the lower limbs. This book provides the overall literature reviews about the human postural control systems (Chapter 1). The development of tools to quantify the human postural control system for stability or robustness is provided (Chapter 2 and 3). This book also investigates how the human postural control systems are affected by perturbations such as aging or load bearing using the developed tools (Chapter 5 and 6). Discussion on the Entropy measures (Chapter 4) and the overall conclusions and the potential future studies (Chapter 7) are provided.