An orthosis for supination and/or pronation of a forearm of a wearer, the orthosis including a base, an upper arm support coupled to the base and configured to secure an upper arm of the wearer, a rotation assembly coupled to the base and including an output member rotatable relative to the base within a rotation plane, and a forearm support member coupled to the output member of the rotation assembly and configured to releasably engage a wrist and the forearm of the wearer, wherein the forearm support member is contoured to receive a thumb of the wearer.