Fin de siècle is French for "End of the Century". The term "turn-of-the-century" is sometimes used as a synonym, but is more neutral (lacking some or most of the connotations described below), and can include the first years of a new century.

The expression Fin de siècle generally refers to the last years of the 19th century. It has connotations of decadence (seen as typical for the last years of a prosperous period, in this case the Belle epoque), and of anticipative excitement about - and/or despair facing - impending change (which is generally expected when a century or time period draws to a close).

That the expression is in French, probably comes from the fact that Fin de siècle is particularly associated to certain French-speaking circles in Paris and Brussels, exemplified by artists like Stéphane Mallarmé, movements like Symbolism, and works of art like Oscar Wilde's "Salomé" (originally written in French, and premiered in Paris) - which connects the idea of Fin de siècle also to the Aesthetic movement. Also Edvard Munch spent some of his time in Paris around the turn-of-the-century, which was his most melancholy period.

In a broader sense the expression fin de siècle is used to characterise anything that has an ominous mixture of opulence and/or decadence, combined with a shared prospect of unavoidable radical change. As such Fin de Siecle is a rather retrospective label and has been added to periods almost at will, the true Fin de Siecle by definition must be that of Europe in 1880-1910, though late Roman literature also has a good claim to this badge.

Note that it is not change itself that is implied in the expression fin de siècle (but only its anticipation), e.g. for the historical 19th century Fin de siècle the radical changes in the cultural and social order would only occur more than a decade after the new century had started (World war I), while by the end of the 19th century the Belle epoque was not even at its height (nor had the Edwardian era, almost seamlessly following the Victorian era, even started). A more recent example of fin de siècle can be found in the Y2K problem: the general turmoil caused by this in itself relatively insignificant technical issue becomes a lot more understandable when acknowledging an underlying fin de siècle mechanism. The War on terror could also be seen to have a definite fin de siècle touch (allegedly anticipating an era without dictators). Even Hitler probably could never have pushed his compatriots thus far in accomplishing his Thousand Year Reich fantasies without the support of fin de siècle-like philosophies (see Millennialism and Nazism), and the fin de siècle atmosphere of the interbellum. Many other 20th century phenomena, e.g. Goth and New Age, could be interpreted as building on at least some fin de siècle ideas.

A good introductory text on the 19th century Fin de siècle is Barbara Tuchman's The Proud Tower.