and Technology (NIST) has a primary function to develop and disseminate standard reference data for the thermophysical properties of fluids and fluid mixtures of interest to the industrial and scientific communities, in this paper we discuss five computerized databases distributed by the Standard Reference Data (SRDI Program of NIST. The databases provide national standards for the properties of pure fluids, an accurate evaluated mixture program focusing on the properties of natural gas mixtures, a predictive package emphasizing hydrocarbon systems up to C_~., a database for refrigerant and prospective alternative refrigerant fluids, and the current scientific thermophysical property surfaces for pure water and steam. The databases include both thermodynamic surfaces and representations for transport properties over broad ranges of temperature, pressure, and composition. We also discuss our current research to improve the standards for air and for aqueous systems including the binary mixture of ammonia and water.