Russia is majority Orthodox Christian, around 70 to 75 percent identifying with the Russian Orthodox Church per most estimates including Pew Research's Religious Composition of the World, 2010-2020, though regular practice is markedly lower, alongside a substantial Muslim minority of roughly 10 percent concentrated among Tatar, Bashkir and North Caucasian peoples including Chechens and Dagestanis, and smaller Buddhist populations among Kalmyks, Buryats and Tuvans, the only traditionally Buddhist peoples in Europe.
Kievan Rus adopted Orthodox Christianity from the Byzantine Empire under Prince Vladimir in 988 CE, a foundational event Russian national memory treats as the baptism of Russia, and the Russian Orthodox Church became closely bound to state power through the Muscovite and later imperial periods, with the tsar recognized as the church's supreme protector after Peter the Great abolished the patriarchate in 1721.
The Soviet period after 1917 pursued state atheism aggressively, destroying or repurposing the great majority of churches, mosques and synagogues, executing or imprisoning large numbers of clergy, and suppressing religious education, a persecution relaxed only significantly during and after the Second World War and largely reversed following the Soviet Union's 1991 collapse, when the Orthodox Church rapidly rebuilt its institutional presence and public standing.