The vast majority of limb loss incidents (~75%) among US Military Service members occur the lower limb.However, restoring sensorimotor function with advanced active prostheses that communicate directly with the intact nervous system falls far behind development of robotic prostheses which are rapidly becoming commercially available to trans-femoral and trans-tibial amputees. The objective of this project is to develop and deploy a fully implantable, self-contained, neurally integrated bidirectional lower limb neuroprosthesis that can be readily incorporated into the body schema and intuitively utilized without cumbersome external components. A total of six subjects (three with trans-tibial and three with trans-femoral limb loss) will be enrolled. Neural stimulation delivered via multi-contact cuff electrodes directly excite the sensory nerves remaining in the residual limb while electromyography (EMG) signals from intramuscular electrodes are interpreted to control the actions of advanced robotic lower limb prostheses. We will examine the impact of integrating sensory feedback with EMG-controlled robotic prostheses on subjective measures of user acceptance and objective measures of balance, gait, and performance during complex mobility tasks in laboratory and during use at home and in community.