Ageing society in many countries has led to an increasing number of stroke and cerebral palsy patients who require rehabilitation therapy. Affected wrist joints often show an increased spasticity and stiffness, caused by impairments of the surrounding muscles and tendons. However, the medical devices for wrist joint assessment and rehabilitation are lacking. The goal of this chapter is to develop and control a robotic orthosis to assist the patient's wrist to perform rehabilitation exercise in a compliant way. A one-degree of freedom (DOF) robotic device with parallel mechanism was designed for the wrist joint by utilising pneumatic artificial muscles (PAMs) that are compliant and lightweight. Mechanical design of the wrist orthosis and the corresponding development of pneumatic control system were presented. A model-based pressure close-loop control strategy was implemented for the PAMs in order to track the trajectory in high-performance. Experiments on the orthosis demonstrated that the robot could assist the hand to move along a torque-sensitive trajectory with small errors and the differential forces were also kept stable.