Plague is a disease that has played an important role in human history; indeed, the word plague has itself become an epithet for infectious disease and the eruption of pest species beyond control. Although bubonic plague (characterized by the development of swollen and painful lymph nodes) is commonly thought of as a disease of the past, plague still represents a significant public health problem, especially in Africa, Asia, and South America (1). Worldwide, a few thousand human cases are reported each year, with a fatality rate between 5 and 15%. The earliest recorded major plague epidemic occurred in China in 224 BCE. Plague appeared in Europe in three long-lasting pandemic waves. The earliest, the Justinian plague, killed several million people, mainly in the Byzantine Empire, during the 6th through 8th centuries. The second wave, the "Black Death," caused some 25 million deaths between the mid-14th century and its culmination in the Great Plague of London in 1665. The third pandemic started in China in the middle of the 19th century and led to 10 million deaths in India alone. Plague is a zoonosis, a disease in which the causative agent primarily resides in wildlife species. It is now known to be caused by the bacterium Yersinia pestis. This bacterium has many varieties, one of which has been linked to the three pandemics (2). The bacterium's principal hosts are wild rodents, and typically fleas are the transmission vector between animals. Only occasionally is Y. pestis transmitted to domestic rodents or other animals in close contact with humans, who may then become infected and develop bubonic plague. In some instances, infected people develop the pulmonary form of the disease, which can then be transmitted from person to person by airborne respiratory droplets. When such transmission fuels an epidemic of pneumonic plague, infected individuals (if untreated) face fatality rates of 95 to 100%. This is most likely the form that dominated past pandemics. Plague and the End of Antiquity: The Pandemic of 541-750 focuses on the Justinian plague. The editor, Lester K. Little (a historian at Smith College in Massachusetts), and 11 other authors, primarily historians, combine findings from a variety of disciplines, including history, archaeology, epidemiology, and molecular biology. They draw on written accounts recorded in Syriac, Greek, Arabic, Latin, and Old Irish as well as excavations of burial pits, abandoned villages, and aborted building projects. The book begins with historiographical and epidemiological overviews, which are followed by discussions of the course and effects of the plague's sporadic appearances in the Near East, the Byzantine Empire, and the Latin West. The final two chapters consider the ecology, evolution, and molecular history of the Justinian plague. The authors' successful integration of insights from many fields provides a thorough account of the pandemic's origins, lethality, waxings, and wanings. The book argues, quite convincingly, that this pandemic's social, economic, political, and religious effects made it a key factor in the fading of Antiquity and the beginning of the Middle Ages. Pestilential Complexities: Understanding Medieval Plague, edited by Vivian Nutton (Wellcome Trust Centre for the History of Medicine at University College London), spotlights the Black Death. The volume brings together skeptics and supporters (drawn from the fields of history, medicine, archaeology, and molecular biology) of the proposition that the infective agent of this second pandemic was Y. pestis. Collectively, the introduction and six essays offer a succinct, multifaceted account of the Black Death. The volume also places the successive waves of the pandemic that broke out in the 1340s into the wider history of the plague, looking back to the Justinian pestilence and forward toward the 19th century. And here too, the authors nicely integrate insights obtained from the several disciplines represented.