Constant (1767-1830) regarded On Religion, worked on over the course of many years, as perhaps his most important philosophical work. He called it "the only interest, the only consolation of my life," and "the book that I was destined by nature to write." On Religion is essential reading and of interest for many reasons. As an analysis of humanity's religious experience, the work is notable for its methodology. Unlike previous writers with dogmatic commitments, whether theological or philosophical, Constant aimed to work with well-established facts and to relate religious forms to their historical contexts and civilizational developments. In this way, he was a precursor of the scientific study of religion. This work demonstrates that principled liberalism can turn a sympathetic as well as analytic eye toward religion, and in an unbegrudging way find an important place for it in free society. There are signs that this is a lesson that contemporary liberalism would do well to relearn.