In this critical biography of J. Gresham Machen, the author sets out to reveal the complexity and broader implications of Machen's religious conservatism. The son of a prominent Baltimore family, Machen studied at leading universities in the United States and Europe and taught for most of his career at Princeton Theological Seminary. Machen's significance, Hart explains, lies in his apparent contradictions. Hart argues that Machen's defence of traditional Christianity - and his criticisms of mainstream Protestantism - actually complemented many of the forces of modernity. Demanding that churches restrict their activities to religious endeavours, Machen rejected the project of preserving Protestant America. His insistence on strict enforcement of Calvinist orthodoxy in the Presbyterian Church went hand in hand with ardently libertarian views on many social and political issues.