Cicero was one of classical antiquity's most prolific, varied and self-revealing authors. His letters, speeches, treatises and poetry chart a political career marked by personal struggle and failure and the collapse of the republican system of government to which he was intellectually and emotionally committed. They were read, studied and imitated throughout antiquity and subsequently became seminal texts in political theory and in the reception and study of the Classics. This Companion discusses the whole range of Cicero's writings, with particular emphasis on their links with the literary culture of the late Republic, their significance to Cicero's public career and their reception in later periods.