This paper presents the design of an underactuated lower body exoskeleton to assist with walking. It reduces the amount of bodyweight going through the user's leg by providing a supporting force to the user that is engaged and disengaged depending on the stage of the gait cycle the user is in. It is engaged when the leg is in stance, effectively pushing between the ball of the foot and the hips, and is disengaged during leg swing. This support force is provided by a linear actuator on each leg that consists of a compression spring, ball screw, and motor. It works by having the motor turn the ball screw, which moves a metal plate to either compress or decompress the spring. The actuator is designed to always be able to extend, to avoid limiting the user's motion. The spring is disengaged while the leg is in swing in order to reduce any impedance to the user's natural stride. The exoskeleton is also designed to minimize any range of motion limitations to reduce its restrictiveness. The exoskeleton was found to be able to provide 19 lbs (85 N) of support to the user per leg. / Master of Science / Exoskeletons are external devices worn to assist the user's natural movement or strength. This paper outlines the design of an exoskeleton that assists the user in walking by providing a supporting force on any leg that the user's weight is on. This effectively reduces the load on the user's legs, which could help reduce leg strain and fatigue. The exoskeleton releases this force when weight is removed from the leg to allow the user to easily swing their leg forward to step. The exoskeleton was designed to minimize limitations to the range of motion of the leg joints while walking, squatting, or sitting to ensure that the exoskeleton did not feel restricting or uncomfortable. Testing revealed that the exoskeleton was able to provide a supporting force of approximately 19 lbs (85 N) to the user per leg and met all the joint range of motion requirements to avoid restrictiveness.