For the past 20 years there has been an active program of research among polymer chemists seeking to prepare thermally stable materials for use as fibers, films, rubbers, adhesives, and other plastic uses. Many types of polymeric molecules have been investigated and the search is still going on. There are, of course, many degrees of thermal stability to be considered. For this report I intend to deal with the polymers which are stable in the range of 300°C and above. This limits the number of materials to be covered to what one can include in a limited survey of the field such as this paper is designed to be.