Silicone rubber for purposes of this review will cover materials based on the polymer polydimethylsiloxane (PDMS). Of necessity, groups other than methyl as substituents on silicon will be included, and changes in the backbone structure from that of pure siloxane will be discussed. Rubbers in which polydimethylsiloxane is only a minor constituent will not be a part of this paper. The definition of what constitutes a rubber becomes blurred as one considers elastoplastic materials and rubbery resins. In this review, a rubber is a material whose properties and function when cured depend principally upon an elastic response to stress. Curing means that a network of crosslinked polymer is established by any one of a number of different vulcanization reactions. Silicone rubber is unique in the large number of choices available for forming crosslinks. A crosslinked network of silicone rubber polymers is relatively weak; hence reinforcement by small-particle active fillers, such as silicas, is essential....