Stroke significantly affects millions of individuals around the world every year, leading to considerable physical impairment and serious long-term disability. Gait is one of the most important daily-life activities affected in stroke victims. The development of an ambulatory lower-limb exoskeleton intended for use in stroke survivors is presented in this paper. It is envisioned as an actuated device in the sagittal plane, capable of producing the necessary torque to move the hip, knee and ankle joints (this latter by means of a variable-stiffness ankle-foot orthosis). An additional passive add/abduction degree of freedom at the hip joint is included, as a way to improve walking balance. A control approach for the actuated joints, which aims to assist the subject only when needed, is also proposed. The main goal of this assistive device is to promote the early incorporation of stroke patients with mobility impairments to a feasible rehabilitation treatment. Such device opens the possibility to study means that might optimize conventional rehabilitation treatment.