An internal shear panel for reducing the tendency of the upper portions of buildings to move relative to the foundation when lateral forces, such as those produced by winds and earthquakes, are applied to the walls. The shear panel is pre-assembled having two vertical posts and two diaphragm members interconnecting the posts. The panel also has an upper and a lower horizontal member that are connected to the posts and the diaphragm members. The lower horizontal member and the posts are configured to be attached via brackets to holdown bolts mounted in the foundation of a building and the upper horizontal member is configured to be attached to an upper plate of the wall. Hence, the shear panel can be installed by connecting the upper horizontal member to the upper portion of the wall and connecting the lower horizontal member to the holdown bolts in the foundation.