The Letters to Brutus (Latin: Epistulae ad Brutum) is a collection of letters from the Roman statesman and writer Marcus Tullius Cicero to Marcus Junius Brutus, the assassin of Julius Caesar. It features some 25 letters written in 43 BC, a year after Caesar's death and a year before Brutus' own suicide following the battle of Philippi.
Free online texts
Latin Library: Epistulae ad Brutum. Latin text, HTML format.
Loebulus. L230N - Cicero -- Letters to His Friends III: Books 13-16. To His Brother Quintus. To Brutus. PDF of public domain Loeb edition in Latin and English.
Perseus: Letters to and from Brutus. Latin text, HTML and XML format.
Wikisource: Epistulae ad Brutum. Latin text, multiple formats.
Wikisource: Letters to Brutus, translated by Evelyn Shuckburgh (1900). Multiple formats.
History of Philosophy without any gaps: Rhetorical Questions: Cicero - podcast by philosopher Peter Adamson.
History of Philosophy without any gaps: Raphael Woolf on Cicero - podcast by philosopher Peter Adamson.
The Great Conversation: Further reading at Tom's Learning Notes
Cicero: Letters to Atticus.
Cicero: Letters to Friends.
Cicero: Letters to Quintus.
Latin resources: Learn to read Latin texts in the original.