Abstract: The panels and mullions of a curtain wall are attached to the frame of the building enclosed by the curtain wall with anchors which permit the frame to shift horizontally and vertically relative to the curtain wall so that the frame and the curtain wall can experience different degrees of racking. Each anchor includes a base member and a displaceable member located in front of the base member. Both members have keyways and are coupled together with a horizontal key that engages the members at their keyways, allowing the displaceable member to shift horizontally relative to the building frame, but preventing it from pulling away from the base member. Each anchor also has a mullion clamp which is attached firmly to one of the mullions. It has a vertical keyway where it is engaged by a key on the displaceable member, thus permitting vertical displacement of the mullion relative to the building frame.