With ceramics prepared from organic precursors, polymers are often formed by thermolysis, and the ceramics are obtained by pyrolysis of the polymer. This paper will cover the NMR methods used to characterize the polymerization as well as the pyrolysis of such polymers. The reticulation rate of such materials is measured on the silicon atoms and on the carbon atoms, leading to a silicon reticulation state and a carbon reticulation state. For the ceramics, the quantification of the SiCxH4−x or SiCxN4−x sites is performed using a priori chemical shift calculation. A measure of the H/C of the free carbon phase at the different temperatures of pyrolysis is presented. This measure uses a absolute determination of hydrogen content in ceramics, more accurate than a classical chemical analysis of hydrogen. The evolution of the reticulation, of the free carbon amount and of the H/C ratio in the free carbon phase will be followed with the temperature.