A critical survey has been made of the values of 16 basic physical constants of rubber in the fields of mechanics, heat, optics and electricity. The value for each constant which seems most reliable has been indicated and, when necessary, has been corrected to the standard conditions of normal atmospheric pressure and a temperature of 25° C. The values have been given for rubber in four different forms: purified hydrocarbon, commercial raw rubber, soft vulcanized rubber containing 2% combined sulfur and hard rubber containing 32% sulfur. The survey indicates that there are significant gaps in present knowledge of the fundamental properties of rubber. In some cases data are lacking, while in many others the best values available are not of the accuracy required for present-day scientific and industrial work. This paper may therefore serve not only as a summary of selected values of the different constants, but also as a basis for the planning of future investigations.