This dissertation proposes a new interpretation for the political engagement of French writers in the Dreyfus Affair between 1897 and 1900. I argue that aesthetics has been undervalued by past scholarship on this question, and analyze the engagement of four very different writers - Emile Zola, Ferdinand Brunetière, Henry Céard and Saint-Georges de Bouhélier - demonstrating that, in each case, their prior aesthetic thought was a vital part of their political discourse on the Affair. This claim involves a rethinking of the relationship between aesthetics and politics as it has usually been conceived, with the aesthetic no longer a reflection of the political, but rather a potential source for it. For each of the writers studied, his literary criticism and theory (dating as far back as the 1860s) are put in dialogue with his writing about the Dreyfus Affair itself through close readings of both corpuses. In each case, attention is paid to the continuities and inversions of central ideas such as individualism, truth, and the Republic, in order to illustrate their structural role in the intellectual world of the fin de siècle. As a result, I have termed the four chapters 'micro-histories of ideas' to convey the way in which individual concerns provide a window onto the major battles of ideas in the France of the early Third Republic.