The structure and properties of various reaction products resulting from the polymerization of carbon disulfide and carbon diselenide are reviewed. In many respect, CSe2behaves like CS2. However, CS2can be polymerized (without a catalyst and in the absence of irradiation) only under high pressure, and this reaction yields a semiconductor. On the other hand, CSe2is easily polymerized under ambient conditions. Depending upon the polymerization conditions, products are obtained which range from insulators to metals and superconductors. Results indicate that (CSe2) reacts to form a head-to-head linear polymer, which thermally decomposes at relatively low temperatures to produce free selenium. This free selenium is the likely origin of the observed superconductivity.