The Cossacks is a novel by Russian novelist Leo Tolstoy, who later earned fame for such novels as War and Peace (1869) and Anna Karenina (1878). Published in 1863—and originally titled Young Manhood—the novel represents about a decade of work on the part of the novelist (who had published just two pieces before this).

The novel begins with a young man named Olenin in the company of his friends as he goes off to join the army. Olenin is described as a "yunker"—a young man of noble birth who volunteers for military service. He has thus far lived a life of pleasure. He has idealistic notions of love, and he dreams of falling in love himself—perhaps with a Circassian woman while in military service in the Caucasus.

Olenin enters into the world of the stanitsa (a Cossack village) and stays with one Dame Ulitka and her family (her husband is a Cossack ensign and schoolteacher who is often absent from the home). Olenin takes note of Maryanka, his hostess's beautiful (though unrefined) daughter, with whom he eventually falls in love. Dame Ulitka, however, tells Olenin that Luka—a respectable young man who once rescued a drowning man—plans to marry Maryanka.

Olenin, who is somewhat ostracized as a guest in the Cossack village, spends time alone and on hunting trips, where, on one occasion, he meets Luka and his Uncle Eroshka. The three develop a mutual respect and friendship. They continue to hunt together, though Luka is stationed at the Caucasian border to defend against the Chechens (a Muslim ethnic group from in the northern part of the Caucasus). Olenin gives Luka a horse in an attempt to befriend him.

Meanwhile, Olenin grows increasingly fond of Maryanka, and finally declares his love for her. She coyly rebuffs him but does not reject his affections entirely. Olenin is encouraged by a fellow Russian, Beletsky, to pursue Maryanka—who has not consummated her relationship with either Olenin or Luka.

The final part of the novel involves a battle between Chechen raiders and a Cossack unit, of which Olenin is a part of. Luka sustains a stomach wound and eventually dies. Maryanka, distraught by her loss of Luka, now outright rejects Olenin's proposal. Olenin leaves to return to Russia, realizing that his hosts (even his friend Eroshka) will continue in their life without him.