Assistive technologies such as robotic and exoskeleton devices are utilized to aid in Activities of Daily Living (ADLs) and in rehabilitation tasks to alleviate and restore some of the lost degrees-of-freedoms (DOFs). However, most of the existing exoskeletons have alignment issues and limited functionality. The fitting and alignment of an exoskeleton with human anatomical joints and limbs are challenging, as the later has joints with a moving axis that generates complex motions. For instance, the shoulder joint does not have a fixed axis of rotation and has more than 3 DOFs, however most of the existing exoskeleton designs simplify the design by modeling the shoulder joint using ball and socket joint or three intersecting hinge joints. Such axes mismatches could cause severe pain and unconfort on the user. And this shows that a new design approach or a modification is needed to address such issues. This thesis is aimed at designing and testing new exoskeleton for upper arm rehabilitation. The designed exoskeleton is equipped with 5-DOF active joints; with four of them associated with the complex shoulder joint movements. The design is assessed for structural stability, functionality, ergonomics for fitting and alignments. The structural analysis was performed in CAD environment with finite element analysis and through prototype model. The effects of fitting and alignment were assessed through a three-stage ergonomic evaluation for the upper limb exoskeleton. The exoskeleton had an overall Rapid Upper Limb Assessment (RULA) score of 3. The effect of fitting and alignment has been assesed through musculoskeletal modeling in OpenSim and actual prototype testing, in both tests, upper arm muscles responded with a similar profile as the one without wearing exoskeleton, indicating that the exoskeleton did not cause any misalignment or out of plane pressure on the muscles.