A portable active fluid-powered ankle foot orthosis. A lower leg mount and a foot bed are pivotally coupled at or proximate to an ankle position. A fluid powered rotary actuator is configured to receive power from a wearable fluid power source and provide controlled force and resistance to aid or inhibit relative rotation of the foot bed and the lower leg mount. An integral controller is provided for receiving data from sensors and controlling the fluid powered rotary actuator to actively assist gait of a user.