In summary, it is probably true to say that the basic mechanisms responsible for the tensile strength of rubbers are now mostly known. Some disagreement exists concerning the exact role played by crystallinity and filler action. Opinions concerning the way in which the fracture propagates through the sample also differ. It is clear that all the present theories concerning tensile strength are inadequate in many ways. Although the basic ideas involved may be quite correct, much refinement in these theories is still needed. They are only rather crude first approximations to a fully successful theory of tensile strength. It is hoped that this review has been successful in pointing out the successes and failures of current theories so that improvements may be made in them.