The concepts and definitions of inorganic polymers, inorganic-organic polymers, and organic-inorganic polymers are summarized in this chapter. These polymers were classified according to the definitions by International Union of Pure and Applied Chemistry (IUPAC). Definitions of representative inorganic polymers are also summarized. The preparation of ceramics from inorganic polymer or inorganic-organic polymer is a useful application of the precursor method. The advantages and disadvantages of the precursor method are summarized.