This edition of Jonson's great Roman tragedy is more intensively researched than any that has previously appeared. The text is based on extensive collation of the 1605 and 1616 versions and takes the earlier version as copy-text. The introduction offers a radically new assessment of Jonson's historiography and his treatment of sources. It provides an explanation for the charge of treason leveled at Jonson over Sejanus and for which he had to answer to the Privy Council. Explanatory notes to the text provide much new information to facilitate a properly informed reading of the play.