The Twelve Caesars is a set of twelve biographies of Julius Caesar and the first 11 emperors of the Roman Empire written by Gaius Suetonius Tranquillus. The book provides valuable information on the heritage, personal habits, physical appearance, lives, and political careers of the first Roman emperors as it mentions details which other sources do not. As with many of his contemporaries, Suetonius took omens seriously and carefully includes reports of omens portending Imperial births, accessions, and deaths. The Twelve Caesars was considered very significant in antiquity and remains a primary source on Roman history. The book discusses the significant and critical period of the Principate from the end of the Republic to the reign of Domitian.

Suetonius (c. 69 after 122 AD) was a Roman historian belonging to the equestrian order who wrote during the early Imperial era of the Roman Empire. His most important surviving work is a set of biographies of twelve successive Roman rulers, from Julius Caesar to Domitian, entitled De Vita Caesarum. He recorded the earliest accounts of Julius Caesar's epileptic seizures. Other works by Suetonius concern the daily life of Rome, politics, oratory, and the lives of famous writers, including poets, historians, and grammarians. A few of these books have partially survived, but many have been lost.