Abstract: The invention relates to a positioning unit for an optical element in a microlithographic projection exposure installation. Said unit comprises a first connection region (A, 22) for connecting to the optical elements, and a second connection region (B, 20) for connecting to an object in the vicinity of the optical elements. At least two levers are connected to the second connection region by means of the respective lever bearing thereof, and the respective load arm thereof is connected to the first connection region by an articulation by means of an intermediate element (31, 33, 36) applied to said articulations. Regulating devices (28, 29) or actuators are arranged on the respective power arms of the levers.