A very compact active x-ray mirror based on the properties of bimorph piezoelectric systems has been developed at the ESRF. The use of such a system as an x-ray focusing device has a number of advantages among which are compactness, low cost, and versatility. As a demonstrative test, a white focused beam of 35 μm has been obtained on an ESRF bending magnet beamline that corresponds to a demagnification of 1/18. A theoretical description of the system behavior is given, and compared with both finite element analysis and interferometric measurements. Examples of more advanced devices are discussed.