In 1967 the geological department of the Doerner-Institute started to advise the German monument offices and museums in questions of stone conservation. To attain the best results possible at the actual state of our knowledge the nature of damage is examined thoroughly by means of thin sections, chemical and x-ray diffraction analysis of salts, tests for bacterias, determination of moisture in walls, etc. From these and from observations on the building we deduce the cause of damage, to elaborate methods of preservation adapted to the peculiar problems. As methods for stone conservation solutions of inorganic salts forming no crusts (like the French MOS-products) are most reliable. Synthetic resins and silicate esters are used only to save heavily decayed objects. The application of waterglasses and related compounds during one hundred years of appli-cation proved to be dangerous for the conservation of monuments. Methods for protection against ground moisture, the execution of plaster and paint, are always elaborated together with the method for stone preservation. A documentation with photos about all of the executed stone conservations exists in the perforated card system of the Doerner-Institute. -- AATA