Novel advanced ceramic materials can be built up from molecular units as precursors which must be cross-linked with each other via a polymerization process yielding a preceramic polymer. A subsequent thermal treatment called thermolysis or pyrolysis transforms this polymer into the ceramic material. The mechanical and the functional properties of the final material strongly depend on the chemistry of the molecular units and on the details of the transformation steps. Therefore, this route enables an adjustment of the processing parameters and a molecular design of the precursors including the usage of appropriate catalysts and of special active or passive fillers. As a result, a real tailoring of materials can be achieved.