"Seventh-Day Men" was the seventeenth-century name given to an emerging and important body of Christians who believed in the strict observance of Saturday, rather than Sunday, as the Sabbath. This is the first-ever fully documented study of these people, who in their heyday were at the center of debate and controversy among the leading writers of the age. This study provides clear evidence that this sabbatarian body of Christians was far more extensive than has so far been recognized, and establishes its considerable significance within the history of the church in the period.