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Polymeric precursors to Si/C/N-ceramics can be obtained by thermal crosslinking of polysilazanes. The precursor is then pyrolysed at a temperature of 1000 °C into the amorphous ceramic. Between 1000 and 2000 °C this amorphous state is transformed into the thermodynamically stable phases. The processes during pyrolysis and crystallization are connected with microstructural conversion. Simultaneously, changes of chemical and physical properties take place. The successive conversion of the atomic coordination during the transformation from the polymer into the amorphous ceramic and finally into the crystalline ceramic was studied using solid-state NMR. 29 Si-, 13 C- and 1 H-spectra were recorded. The result is a detailed report of the reactions and changes in structure occuring during ceramization of a polyhydridomethylsilazane and crystallization of its ceramic residue. Furthermore, the amorphous state of this material was compared with a polyvinylsilazane-derived amorphous ceramic.