This book is a study of the various claims to authority made by the ancient Greek and Roman historians throughout their histories and is the first to examine all aspects of the historian's self-presentation. It shows how each historian claimed veracity by imitating, modifying, and manipulating the traditions established by his predecessors. Beginning with a discussion of the tension between individuality and imitation, it then categorises and analyses the recurring style used to establish the historian's authority: how he came to write history; the qualifications he brought to the task; the inquiries and efforts he made in his research; and his claims to possess a reliable character. By detailing how each historian used the tradition to claim and maintain his own authority, the book contributes to a better understanding of the complex nature of ancient historiography.