With this edition of book I P. J. Rhodes provides the 'prequel' to his editions of Thucydides' books on the Archidamian War (II, III and IV. 1 - V. 24). As before he provides an Introduction on Thucydides' history and on the Peloponnesian War, a Greek text with selective critical apparatus and facing translation, and a commentary which should be useful both to specialists and to readers with litttle or no Greek, and which assumes no previous acquaintance with Thucydides. Matters of text and language are discussed where necessary, but the emphasis is on Thucydides' subject-matter -- the Peloponnesian War presented as the greatest war in Greek history, and accounts of the events directly leading to the war and of the growth of Athenian power since the Persian Wars which explain why this war between the two great powers of fifth-century Greece was fought -- and on the way in which he has treated it.