Manufacturing of bulk ceramic components from materials in the system Si-Me-C-N-O (Me = Ti, Cr, V, Mo, Si, B, CrSi2, MoSi2, etc.) from preceramic organosilicon polymers - such as poly(carbosilanes), poly(silazanes), or poly(siloxanes) - has become possible by incorporating reactive filler particles into the liquid or solid polymer pre-cursor. During pyrolytic decomposition of the polymer matrix, the filler particles react with carbon from the polymer precursor or nitrogen from the reaction gas atmosphere to form new (oxy)carbide or (oxy)nitride phases embedded in a nanocrystalline Si-O-C(-N) matrix. The selective expansion encountered in the filler phase reaction can be used to compensate for the polymer shrinkage upon pyrolytic conversion. The formation of a transient pore net-work between 400° and 1000°C is governed by the polymer decomposition as well as the filler particle reaction kinetics. Thus, the properties of the oxycarbonitride composite materials can be tailored by controlling the microstructures of the polymer-derived matrix phase, the filler network, and the residual porosity. Near-net-shape forming of bulk ceramic components, even with complex geometry, is possible, making novel applications of polymer-derived bulk materials in biomedical, electrical, and mechanical fields highly interesting.