This investigation consists of updates to the chronology of Achaemenid Persia (539 BCE-304 BCE). The state of Achaemenid chronology was the subject of a series of studies published by this writer about ten to fifteen years ago. Newly emerged evidence has necessitated the present updates. Errata in those earlier studies are listed in an appendix. The focus of the present investigation is on what is new. A comprehensive statement on Achaemenid chronology that progresses from first principles and combines all that is new with all that is old remains desirable. Few historical events are as transforming in the history of nations as the death of one ruler and the accession of the next. Accordingly, the chronology of regnal transitions deserves special attention in the study of ancient chronology. This study provides updates for the chronology of nine regnal transitions in the Achaemenid empire: Xerxes I to Artaxerxes I (465); Artaxerxes I to Darius II (424-23); Darius II to Artaxerxes II (405/4); Artaxerxes IIto Artaxerxes III (359/58); Artaxerxes III to Arses (338); Arses to Darius III (336/35); Darius III to Alexander III (331); Alexander III to Philip Arridaios (323); and Arridaios to Alexander IV (317). A comprehensive tabulation of the regnal years of the final years of the empire (340-304) is presented at the end.