The fourth edition of "The Chemistry of the Actinide and Transactinide Elements" comprises all chapters in volumes 1 through 5 of the third edition (published in 2006) plus a new volume 6. To remain consistent with the plan of the first edition, to provide a comprehensive and uniform treatment of the chemistry of the actinide and transactinide] elements for both the nuclear technologist and the inorganic and physical chemist, and to be consistent with the maturity of the field, the fourth edition is organized in three parts.