Lessons of October (Russian: Уроки Октября) is a polemical essay of about 60 printed pages in length by Leon Trotsky, first published in Moscow in October 1924 as the preface to the third volume of his Collected Works. The essay was harshly critical of the purported revolutionary failings of Grigory Zinoviev and Lev Kamenev, two key members of the collective leadership which briefly ruled Soviet Russia in the months after the death of V. I. Lenin. Publication of the essay was used as a pretext for the Soviet leadership to isolate and attack Trotsky, whom the leadership mutually perceived as a threat to accede to supreme power.
In subsequent years Trotsky's essay was reprinted several times under its own covers by the international Trotskyist movement.