Abstract: A five bar spherical serial closed loop linkage includes a first link, and a second link rotatably mounted to the first link about a first axis of rotation, the axis of rotation passing through a center of a sphere defined by the linkage. A third link rotatably mounts to the second link about a second axis of rotation passing through the center of the sphere. A fourth link rotatably mounts to the third link about a third axis of rotation passing through the center of the sphere. A fifth link rotatably mounts to the fourth link about a fourth axis of rotation passing through the sphere's center, and rotatably mounts to the first link about a fifth axis of rotation passing through the center of the sphere. An instrument mounts to the linkage and typically is aligned with the spherical center. Two motors having encoders drive the two degrees of freedom and are in communication with a central processor or controller to control movement of the linkage.