This chapter reviews pyrolyzability of preceramic polymers. The pyrolyzability of a given precursor should then be considered from a practical point view of whether the precursor gives the desired composition and with reasonably high yield. A precursor should, therefore, have at least two inherent characteristics: latent reactivity and branched structures. The latent reactivity can provide the opportunity for cross-linking and thereby provide for both maintaining appropriate shape during processing and high ceramic yield. The changes in density are also discussed. The pyrolyzability of a fair number of silicon carbide (SiC), silicon nitride (Si3N4), and Si3N4/SiC precursors are examined. The data includes approximate structures/representations of the precursors, the pyrolysis conditions, and the compositions of the residues. Pyrolysis data on boron-containing precursors with various structures are tabulated. Conversion of a precursor to its respective ceramics involves numerous reactions. During the pyrolysis process, volatile organic species are generated and eliminated, which may drastically lower the ceramic yield. Cross-linking of the preceramic polymers before pyrolysis is often necessary to help retention of the ceramic elements in the solid states, thereby improving the desirable ceramic yields.