This is a study of the Protestant utopian movement that began in Germany, inspired in large measure by the writings of Johann Valentin Andreae and came to England through the efforts of the emigre Samuel Hartlib. The first chapters examine Andreae's utopian writings, including the Rosicrucian manifestos, as part of his lifelong commitment to found a Societas Christiana, a spiritual elite that would improve religious and intellectual life. His writings sparked a transnational movement in early modern Europe. The most significant of the German learned societies are discussed: The Societas Ereunetica, Unio Christiana and Antilia. The latter chapters consider Hartlib's English circles and various utopian and learned societies in the 1650s. The text seeks to contribute to the understanding of the role that "secret" societies and epistolary networks had in the republic of letters.