A memoir (ˈmɛm.wɑr; me.mwaʁ, ) is any nonfiction narrative writing based on the author's personal memories. The assertions made in the work are thus understood to be factual. While memoir has historically been defined as a subcategory of biography or autobiography since the late 20th century, the genre is differentiated in form, presenting a narrowed focus, usually a particular time phase in someone's life or career. A biography or autobiography tells the story "of a life", while a memoir often tells the story of a particular career, event, or time, such as touchstone moments and turning points in the author's life. The author of a memoir may be referred to as a memoirist or a memorialist.
Memoirs have been written since the ancient times, as shown by Julius Caesar's Commentarii de Bello Gallico, also known as Commentaries on the Gallic Wars. In the work, Caesar describes the battles that took place during the nine years that he spent fighting local armies in the Gallic Wars. His second memoir, Commentarii de Bello Civili (or Commentaries on the Civil War) is an account of the events that took place between 49 and 48 BC in the civil war against Gnaeus Pompeius and the Senate. The noted Libanius, teacher of rhetoric who lived between an estimated 314 and 394 AD, framed his life memoir as one of his literary orations, which were written to be read aloud in the privacy of his study. This kind of memoir refers to the idea in ancient Greece and Rome, that memoirs were like "memos", or pieces of unfinished and unpublished writing, which a writer might use as a memory aid to make a more finished document later on.
The Sarashina Nikki is an example of an early Japanese memoir, written in the Heian period. A genre of book writing, Nikki Bungaku, emerged during this time.
In the Middle Ages, Geoffrey of Villehardouin, Jean de Joinville, and Philippe de Commines wrote memoirs, while the genre was represented toward the end of the Renaissance, through the works of Blaise de Montluc and Margaret of Valois, that she was the first woman to write her Memoirs in modern-style.