This volume will come as something of a surprise to someone accustomed to thinking of Kant as a prime example of an armchair philosopher. For although it is true that he never travelled far beyond Königsberg and is famous for having emphasized (synthetic) a priori cognition, that is, (substantive) cognition of the world that can be obtained independently of any particular sensory experiences, Kant wrote extensively throughout his career on a broad range of topics that we today would consider part of natural science. It is not uncommon to recognize that Kant produced important publications that bear on natural science in some way, publications that find a home in other volumes in the Cambridge Edition of the Works of Immanuel Kant. For example, Kant’s relatively brief Physical Monadology (1756) appears as part of Theoretical Philosophy, 1755–1770. The more substantial Metaphysical Foundations of Natural Science (1786), which attempts to show how the abstract principles argued for in the Critique of Pure Reason can be realized in more specific principles by having an empirical concept of matter applied to them, can be found in Theoretical Philosophy after 1781. And the remarks Kant composed late in his career (in the 1790s and beyond) on the transition from the principles established in the Metaphysical Foundations of Natural Science to empirical natural science are available in the Opus postumum. However, even an awareness of these important works still falls short of an acknowledgement of the breadth and depth of Kant’s interests in natural science. For one, Kant writes on an even wider range of specific topics in the domain of natural science, such as the causes of earthquakes, the nature of fire, the rotation and ageing of the Earth, theories concerning moisture in winds, and the appearance and nature of comets and other meteorological phenomena. For another, he is not content to provide brief interventions on narrowly defined scientific questions, but also undertakes foundational and comprehensive projects in natural science, such as determining the conservation of force in nature, formulating the proper laws of motion, developing a full-scale Newtonian cosmogony, and offering an expansive physical geography.