One of the most striking developments of the eighteenth century in France is the emergence of the epistolary form as a dominant vehicle for cultural and literary expression. Almost any kind of narrative can be found in letter form during the Enlightenment; by the century’s second half, the letter has become an all-purpose literary omnibus and serves, moreover, as the basic structural component of many of the period’s most widely-read novels. This work explores the implications of the letter’s popularity in terms of the eighteenth century’s intellectual climate, and concludes that the epistolary form is particularly well-suited to an expression of the Enlightenment’s ideological concerns.