The Kondratieff Wave, also known as the Kondratieff Cycle or Long Wave, is a theoretical economic concept proposed by the Russian economist Nikolai Kondratieff in the 1920s. It suggests that capitalist economies undergo long-term cycles of expansion and contraction, lasting approximately 50 to 60 years.

According to the theory, these waves consist of four main phases: a period of economic upswing and growth (spring), followed by prosperity and expansion (summer). Then, there is a phase of economic downturn and contraction (autumn), and finally, a period of depression and low economic activity (winter). Each of these phases is characterized by various economic trends, technological advancements, and societal changes.

Though controversial and not universally accepted, the Kondratieff Wave has been influential in economic discussions. Some proponents argue that understanding these long cycles can help predict future economic trends and guide policy decisions, while critics question the regularity and predictability of such waves in modern economies.