Wearable exoskeletons are one of the primary advancements that help to alleviate the effects of spinal cord injury (SCI) including degenerative changes in organs of the body. Artificially stimulating the wearer's muscles to move his or her limbs has the additional benefit of maintaining musculature and improving circulation. The exoskeleton system developed in this project will use this "muscles first" approach with additional assistive power from electric motors on an as-needed basis. The major contribution of the project is that it will ensure stability of the person during standing and at normal walking speeds. The result will be that persons with SCI will be more comfortable standing and walking more erect and, therefore, be more socially engaged. The societal impact of this will be that persons with SCI will be better able to work and participate in social and leisure activities and in other behaviors associated with independent and productive lifestyles. In addition, Cleveland area high school students will be involved in the project and learn about human biomechanics and engineering methods. This project addresses how cyber physical walking systems (CPWS) can be designed to be safe, secure, and resilient despite a variety of unanticipated disturbances and how real-time dynamic control and behavior adaptation can be achieved in a diversity of environments. Specifically, a CPWS will be developed that seamlessly integrates: (1) a person who has a spinal cord injury (SCI) with intact and excitable lower motor nerves; (2) an exoskeleton with controllably locked/unlocked and/or passively damped joints; (3) DC motors for need-dependent joint power assistance; and (4) computational algorithms that continuously and automatically learn to improve standing and walking stability. In this "muscles first" approach, functional neural stimulation (FNS) provides most of the joint torques for walking and for maximum health benefits and, thus, as-needed assistive joint motors may be small and lightweight. The specific aims are 1) Assist the user's muscles on an as-needed basis and for high-bandwidth stability control by adding small, low passive-resistance motor/transmission pairs to our CPWS; 2) Develop computational algorithms for system estimation, machine learning and stability control for SCI users standing and walking with a CPWS while minimizing upper extremity effort; 3) Verify system performance with able-bodied individuals and assess upper extremity reduction and balance control in individuals with SCI using the CPWS for standing and ambulation.