Based on the IAPWS Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam (IAPWS-IF97) by ASME Research and Technology Committee on Water and Steam in Thermal Systems, Subcommittee on Properties of Steam. The main update for this Third Edition is the incorporation of the new IAPWS formulation adopted in 2011 for the thermal conductivity of water and steam. This is reflected in new Tables S-9, S-10, U-9, and U-10, along with new Figures S-4, S-5, U-4, and U-5 and revision of Appendix B. The thermodynamic property information is unchanged from the Second Edition. The authors also made minor updates to some of the background text and references.