Organotin compounds are characterized by the fact that they contain at least one direct bond between tin and carbon, Sn-C. The compounds are classified as mono-, di-, tri-, or tetraorganotins, according to whether there are 1, 2, 3, or 4 tin-carbon bonds in the molecule. Each class of compound has specific properties which have proved of interest to industry, for example mono-and diorganotins have catalytic properties and can stabilize plastics such as PVC against the degredative effects of heat and light. The triorganotins are powerful biocides. Some of these compounds can be used to preserve wood.