Nikolai Dmitriyevich Kondratiev (; also Kondratieff; Russian: ??????´? ???´??????? ??????´????; 4 March 1892 – 17 September 1938) was a Soviet economist, a proponent of the New Economic Policy (NEP), which in the 1920s promoted small private, free-market enterprises in the Soviet Union.
He is best known for proposing the theory that Western capitalist economies have long term (50-to-60-year) cycles of boom followed by depression.
These business cycles are now called "Kondratiev waves".