Medicine and astronomy are the oldest of all the sciences. They appear at first glance to be the original "odd couple." Their union gave birth to a progeny that populated the Western world for more than two millennia. From an historical perspective, their marriage and mutual influence is undeniable. Cosmology and cosmogony, as natural philosophical aspects of astronomy, have gone hand in hand with the science of medicine from time immemorial. Indeed, medicine and the pseudoscience of astrology were for centuries inseparable. The ancients began the embryonic search for answers to questions that had puzzled humans for eons. No systematic approach to the nature of the universe was undertaken until the Sumerians, the Babylonians, and the Greeks began the quest for wisdom. The Greeks, beginning with Thales in the 6th century B.C.E., sought a unifying principle to explain the world as a whole. Because cosmology and medicine were among the few known sciences in ancient times, it was natural that these two apparently disparate disciplines should be combined to provide the theoretical basis of medicine - foundations that were to survive for nearly 2,400 years.This scientific structure rested firmly on the ancient principles of cosmology, astronomy, and the concept of universal harmony. This book tells the tale of these theoretical underpinnings and how they influenced humankind's efforts to maintain health and fight disease. Ultimately, the system was fundamentally flawed. Nonetheless, it lingered on for centuries beyond what common sense tells us it should have. Few comprehensive analyses of the relationship between cosmology and medicine have been undertaken in the astronomical or medical literature. For better or for worse, cosmological principles have had profound effects on the theory and practice of medicine over the centuries. It is time for historians, astronomers, physicians, and philosophers to acquaint themselves with the impact early cosmology has had on medicine. Awareness of this linkage can help us better understand not only past but present-day medicine. This book is a fascinating review of the historical roots of the medical tradition.