In an internal combustion engine including cylinders arranged in a housing, a crankshaft, pistons disposed in the cylinders so as to be movable by the crankshaft, and a device for varying a compression ratio of the internal combustion engine wherein the device, for varying the compression ratio, includes an adjusting structure which varies the effective length of a connecting rod of the piston, the lift of the crankshaft or the position of the cylinder with respect to the center of the crankshaft, an operating structure is provided by rotation of which the position of the adjusting structure can be controlled, and a drive device for controlling the operating structures contains a coupling mechanism with an integrated brake function, whereby h the adjusting structure can either be placed in operative connection with the crankshaft or can be blocked.