The Brusilov Offensive (Russian: Брусиловский прорыв Brusilovskiĭ proryv), also known as the June Advance, was the Russian Empire's greatest feat of arms during World War I, and among the most lethal battles in world history. Prof. Graydon A. Tunstall of the University of South Florida called the Brusilov Offensive of 1916 the worst crisis of World War I for Austria-Hungary and the Triple Entente's greatest victory. It was a major offensive against the armies of the Central Powers on the Eastern Front, launched on June 4, 1916, and lasting until late September. It took place in what today is Ukraine, in the general vicinity of the towns of Lemberg, Kovel and Lutsk. The offensive was named after the Russian commander in charge of the Southwestern Front, Gen. Aleksei Brusilov.

Early in 1916 France called upon Russia to help relieve the pressure on Verdun by launching an offensive against the Germans on the Eastern Front, hoping Germany would transfer more units to the East to cope with the Russian attack. The Russians responded by initiating the disastrous Lake Naroch Offensive in the Vilno area, during which the Germans suffered only one-fifth as many casualties as the Russians. Gen. Aleksei Brusilov presented his plan to Stavka, the Russian high command, proposing a massive offensive by his Southwestern Front against the Austro-Hungarian forces in Galicia. The main purpose of Brusilov's operation was to take some of the pressure off French and British armies in France and the Italian Army along the Isonzo Front and, if possible, to knock Austria-Hungary out of the war.

World War I (WWI), which was predominantly called the World War or the Great War from its occurrence until 1939 (World War II), and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918. It involved all the world's great powers, which were assembled in two opposing alliances: the Allies (based on the Triple Entente of the United Kingdom, France and Russia) and the Central Powers (originally centred around the Triple Alliance of Germany, Austria-Hungary and Italy; but, as Austria–Hungary had taken the offensive against the agreement, Italy did not enter into the war). These alliances both reorganised (Italy fought for the Allies), and expanded as more nations entered the war. Ultimately more than 70 million military personnel, including 60 million Europeans, were mobilised in one of the largest wars in history. More than 9 million combatants were killed, largely because of enormous increases in lethality of weapons, thanks to new technology, without corresponding improvements in protection or mobility. It was the sixth-deadliest conflict in world history, subsequently paving the way for various political changes such as revolutions in the nations involved.

Aleksei Alekseevich Brusilov (Russian: Алексе́й Алексе́евич Бруси́лов, Aleksey Alekseyevich Brusilov) (19 August [O.S. 31 August] 1853 – 17 March 1926) was a Russian general most noted for the development of new offensive tactics used in the 1916 offensive which would come to bear his name. The innovative and relatively successful tactics used were later copied by the Germans. His war memoirs were translated into English and published in 1930 as A Soldier's Notebook, 1914–1918.

Brusilov was born in Tiflis (now Tbilisi, Georgia). His father was Russian, his mother, Anna Luiza Niestojemska, was Polish. Three generations of Brusilov's had served as officers in the Tsar's army, his grandfather fighting in the defence against Napoleon's invasion of 1812. His father rose to the rank of Lieutenant General before dying of tuberculosis in 1856. Brusilov's mother died shortly afterwards, and the young orphan was raised by relatives in Kutaisi.

He was educated at home until at the age of 14, he joined the Imperial Corps of Pages in Saint Petersburg in 1867. At the end of his first year, a tutor remarked of Brusilov, "his nature is brisk and even playful, but he is good, straight-forward and clean-living. Of high ability, but inclined to be lazy."