Historization of Time – An Excursion in Historical Theory What is time to historians? This was not a crucial question when modern academic history was born, but since the mid-20th century, ‘historical time’ has increasingly been thematized in historical theory. This article presents some key contributions to this development, from the Annales School and its critique of the temporality in the history of events, through ideas of temporality and layers of time in the historical theory of Reinhart Koselleck, the radical conception of time found in the writings of Michel Foucault, connections to historization of space in global and postcolonial history to recent contributions on historical time in the light of the Anthropocene. On this ground, the article concludes that the so-called temporal turn is a heterogeneous phenomenon. Historical theory is not offering one theory of historical time, but a variety of theories that have been developed on very different theoretical foundations and in very different historical contexts. The most prominent trend in these debates have been that the one-dimensional idea of time as a line has been substituted with theories about layers of time, typically expressed in geological metaphors.