After epoxy resins and polyimides, cyanate esters arguably form the most well-developed group of high-temperature, thermosetting polymers. They possess a number of desirable performance characteristics which make them of increasing technological importance, where their somewhat higher costs are acceptable. The principal end uses for cyanate esters are as matrix resins for printed wiring board laminates and structural composites. For the electronics markets, the low dielectric loss characteristics, dimen­ sional stability at molten solder temperatures and excellent adhesion to conductor metals at temperatures up to 250°C, are desirable. In their use in aerospace composites, unmodified cyanate esters offer twice the frac­ ture toughness of multifunctional epoxies, while achieving a service tem­ perature intermediate between epoxy and bis-maleimide capabilities. Applications in radome construction and aircraft with reduced radar signatures utilize the unusually low capacitance properties of cyanate esters and associated low dissipation factors. While a number of commercial cyanate ester monomers and prepoly­ mers are now available, to date there has been no comprehensive review of the chemistry and recent technological applications of this versatile family of resins. The aims of the present text are to present these in a com­ pact, readable form. The work is primarily aimed at materials scientists and polymer technologists involved in research and development in the chemical, electronics, aerospace and adhesives industries. It is hoped that advanced undergraduates and postgraduates in polymer chemistry and technology, and materials science/technology will find it a useful introduction and source of reference in the course of their studies.