Tracing the origins of our contemporary concern for authenticity to the writings of 18th century philosopher Jean-Jacques Rousseau, this book explores the key thinkers writing in the wake of Rousseau's emphasis on sincerity, namely Friedrich Nietzsche and Martin Heidegger, to show that their acceptance of authenticity as an ideal for humanity was ambiguous at best. This volume also covers representative authors in the earlier history of philosophy, such as Plato, Niccolo Machiavelli, Francis Bacon, and John Locke.