Smallpox inoculation in the eighteenth century was the genesis of modern immunology. This new method of purposely contracting a disease in order to secure protection from it was an empirical folk practice from the New East that ran counter to traditional European habits of thought in both medicine and religion. Based on diligent research in all available sources, this detailed study brings into relief the significant factors that made smallpox inoculation acceptable to Western Europeans--namely, the increasing threat and fear of the disease, particularly among the upper classes; a strong program led by members of such respected scientific groups and the Royal Society in London and the Academic Royale des Sciences in Paris; the interest and participation of both the English and French royal families who furnished an example for their subjects to emulate. In presenting this account of an important development in medical history Genevieve Miller offers evidence to prove that, contrary to the usual view, most religious leaders were not opposed to the practice of inoculation and that a number of them were active proponents. She also points out how, in the sphere of medical thought, experience with inoculation clarified ides concerning the etiology of smallpox by supplying proof that it originated with a specific material substance introduced into the human body from without.