Tadeas Hajek of Hajek (1526–1600), Latinized as Thaddaeus Hagecius ab Hagek/Hayek, was a key figure in early scientific debates not only in his native Bohemia. A versatile scholar and polymath, he was prolific in medicine, botany, mathematics and astronomy. Modern interpreters tended to point out his astronomical interpretations to emphasize his greatest achievements and his “modernity.” However, Hajek also drew extensively on traditional arts such as alchemy, astrology and metoposcopy. In this volume, the contributors study various aspects of Hayek’s thought to present a less tendentious intellectual portrait of him in the context of his times. Even from this more adequate perspective, he remains an important figure in the dialectical process of transmitting ideas whose influence extended far beyond the Czech lands.