This volume is the fourteenth of the series “Chemical Thermodynamics” published by the OECD Nuclear Energy Agency. It is the second update of the critical reviews published, successively, in 1992 as Chemical Thermodynamics of Uranium, in 1995 as Chemical Thermodynamics of Americium, in 1999 as Chemical Thermodynamics of Technetium, in 2001 as Chemical Thermodynamics of Neptunium and Plutonium and in 2003 as the first Update on the Chemical Thermodynamics of Uranium, Neptunium, Plutonium, Americium and Technetium. A team, composed of nine internationally recognised experts, has critically reviewed all the relevant scientific literature for the above mentioned systems that has appeared since the publication of the earlier volumes. The results of this assessment, carried out following the Guidelines of the Thermochemical Database Project, have been documented in the present volume, which contains new tables of selected values for formation and reaction data and an extensive bibliography. The database system developed at the NEA Data Bank ensures consistency within the recommended data sets. This volume will be of particular interest to scientists carrying out performance assessments of deep geological disposal sites for radioactive waste.