War and Peace[a] is a literary work by Russian author Leo Tolstoy. Set during the Napoleonic Wars, the work mixes fictional narrative with chapters on history and philosophy. First published serially beginning in 1865, the work was rewritten and published in its entirety in 1869. It is regarded as Tolstoy's finest literary achievement and remains an internationally praised classic of world literature.

The novel chronicles the French invasion of Russia and the impact of the Napoleonic era on Tsarist society through the stories of five Russian aristocratic families. Portions of an earlier version, titled The Year 1805,were serialized in The Russian Messenger from 1865 to 1867 before the novel was published in its entirety in 1869.

Tolstoy said that the best Russian literature does not conform to standards and hence hesitated to classify War and Peace, saying it is "not a novel, even less is it a poem, and still less a historical chronicle". Large sections, especially the later chapters, are philosophical discussions rather than narrative. He regarded Anna Karenina as his first true novel.