Fin de siècle (French: [fɛ̃ də sjɛkl]) is a French term meaning "end of century,” a phrase which typically encompasses both the meaning of the similar English idiom "turn of the century" and also makes reference to the closing of one era and onset of another. Without context, the term is typically used to refer to the end of the 19th century. This period was widely thought to be a period of social degeneracy, but at the same time a period of hope for a new beginning. The "spirit" of fin de siècle often refers to the cultural hallmarks that were recognized as prominent in the 1880s and 1890s, including ennui, cynicism, pessimism, and "a widespread belief that civilization leads to decadence.”

The term fin de siècle is commonly applied to French art and artists, as the traits of the culture first appeared there, but the movement affected many European countries. The term becomes applicable to the sentiments and traits associated with the culture, as opposed to focusing solely on the movement's initial recognition in France. The ideas and concerns developed by fin de siècle artists provided the impetus for movements such as symbolism and modernism.

The themes of fin de siècle political culture were very controversial and have been cited as a major influence on fascism and as a generator of the science of geopolitics, including the theory of Lebensraum. Professor of Historical Geography at the University of Nottingham, Michael Heffernan, and Mackubin Thomas Owens wrote about the origins of geopolitics:

The idea that this project required a new name in 1899 reflected a widespread belief that the changes taking place in the global economic and political system were seismically important.

The "new world of the Twentieth century would need to be understood in its entirety, as an integrated global whole". Technology and global communication made the world "smaller" and turned it into a single system; the time was characterized by pan-ideas and a utopian "one-worldism," proceeding further than pan-ideas.

What we now think of geopolitics had its origins in fin de siècle Europe in response to technological change ... and the creation of a "closed political system" as European imperialist competition extinguished the world's "frontiers".

The major political theme of the era was that of revolt against materialism, rationalism, positivism, bourgeois society, and liberal democracy. The fin-de-siècle generation supported emotionalism, irrationalism, subjectivism, and vitalism, while the mindset of the age saw civilization as being in a crisis that required a massive and total solution.