An actuating unit for an electromechanically actuatable disk brake for motor vehicles consists essentially of a drive unit (1), i.e., an electric motor (11); an actuating element (7), by means of which one (4) of two friction linings (4, 5) mounted with limited freedom of movement in a brake caliper can be brought into engagement with a brake disk (6); and a first and a second reducing gear (2, 3). An electronic controller (8), which serves to drive the electric motor (11), is assigned to the actuating unit. To realize an actuating unit of compact axial dimensions which is also optimally designed with respect to packaging, at least part of the electronic controller (8) is mounted between the electric motor (11) and the housing (25) which holds the second reducing gear (3).