Herman Boerhaave, holder of three professorships in medicine, botany and chemistry at the University of Leiden, was the most important medical teacher after Galen. His fame reached all over Europe and further afield. Reputedly, a letter from China addressed to 'Mr. Boerhaave, Physician in Europe' was even delivered to Boerhaave's door. Boerhaave was also known as a very religious man. Yet, historians of science and medicine have not paid much attention to Boerhaave's Calvinism. They have stressed the mechanical aspects of his medicine but have neglected his religious beliefs and those of his viewpoints that are alien to modern science. However, this book shows that Boerhaave's natural philosophy - his chemistry and alchemy as well as their uses in medicine - and methodology are all rooted in his Calvinism. In particular, Boerhaave's ideas on the divine nature of fire, the chemical theory of menstrua and the theory of seminal principles demonstrate that Boerhaave presented a Calvinist picture of the world in which the wisdom of God can be seen in the powers peculiar to every creature.