This book explores changes in the values and ideas of a large part of the political Left in recent decades. The author identifies that a questioning of the merits of economic growth; an ideal of environmental sustainability overriding the old radical visions of material abundance; a critique of instrumental reason; a suspiciousness towards universalist claims; and an attachment to subjective and pluralistic identities, have been dominant in the narratives of the Leftist milieu and of social movements. Yet the author suggests that such changes, known as `lifestyle activism', could be understood in a different way, one characterised by suspiciousness towards the belief that human action guided by reason can lead society towards a future that will be better and more affluent. Using a range of case studies from the 1960's to the present day anti-austerity movement, Sotirakopoulos argues that the New Left and its ideological heirs could be understood not so much as a continuation, but as an inversion from the Old Left and, most importantly, from humanistic visions of modernity. The book will therefore be ideal reading for students and researchers of political sociology, radical politics, modern political ideologies, contentious politics and political theory and to scholars of new social movements and the New Left.