The performance of rubber crumb in rubber compound and asphalt modification applications depends upon particle size, surface area, and chemical composition. For routine estimation of size and surface area, sophisticated methods including BET nitrogen adsorption and image analysis have limited applicability. The BET technique is capable of further improvement if argon is substituted for nitrogen and degassing of the crumb can be effectively achieved, and if more realistic programs for the estimation of S/V are developed. However, for simple quality control of particle characteristics, low magnification microscopic examination, CTAB titrations, sieve analysis and estimation of bulk density would appear to be adequate. For rubber modification where maximum performance is not required, most crumb can be used at low levels, but fine crumb with high specific surface area is best. For critical applications, extremely fine crumb, or crumb which has undergone chemical modification to improve adhesion or compatibility, would be required, and these steps would lower the economic incentive for recycling. A controlled study of crumb dewetting using individual particles in a model matrix would contribute to an understanding of tensile behavior. For asphalt applications, chemical composition and surface area are more important than particle size in controlling elastic recovery. However, other parameters, including foam development, stability of rubber with time of digestion, and economic factors are also important. Before predictable behavior in asphalt can be achieved, identification and possibly segregation of scrap may be required.