During his lifetime, Octavius Brooks Frothingham was known as a popular New York City preacher, writer, and promoter of radical or free religion. Eloquent and inspiring, as an orator and teacher he was often compared to Ralph Waldo Emerson, while many considered him Theodore Parker's heir as the champion of free religion. In his last twenty years, he wrote frequently on historical-biographical subjects related to New England Unitarianism and Transcendentalism.

Despite his extensive publication (fourteen books and hundreds of sermons and articles), his modern reputation rests primarily on Transcendentalism in New England: A History (1876). Defining Transcendentalism as a philosophical system, a "spiritual" or "intuitive philosophy," Frothingham focused on its European context and roots, described its "tendencies," and wrote sketches of some of its major figures, most of whom were still living. The book stands in the middle of his New England trilogy. He explores the American roots of...