The data in the ACerS-NIST Phase Equilibria Diagrams Database, jointly copyrighted by NIST and The American Ceramic Society, provide maps of the equilibrium chemical and structural behaviors exhibited by inorganic systems and provide critical starting information for the rational design of materials processing schemes, for quality assurance efforts, and for optimization of the physical and chemical properties of advanced materials. The contents of this database consist of approximately 25,000 equilibrium phase diagrams presented in 17,866 critically evaluated entries (PED Figures). The materials covered include a wide range of non-organic material-types including oxides and mixed systems with oxides, chalcogenides (sulfides, selenides, tellurides), pnictides (N, P, As, Sb, Bi), actinides (U, Pu, Th) and actinide-surrogates (Ce), oxycation systems (e.g. molybdates, vanadates), semiconductors (Si, Ge, Sn), group 3 systems (B, Al, Ga, In, Tl), and salts including mixed systems with salts. The data are pertinent to a wide variety of applications including optoelectronics, thermal-barrier coatings, sensors, energy converters, nuclear waste reprocessing, nuclear reactors, photovoltaics, pigments, fuel cells, catalysts, thermoelectrics, capacitors, transducers, thermoluminescence, molten-salt batteries, photovoltaics, electrolytic refining, and semiconductor manufacturing. A free demonstration CDROM which includes a comprehensive Cumulative Index for the entire database is available upon request or can be downloaded from the website http://www.nist.gov/srd/nist31.cfm.