The idea of preparing a new critical edition of Elisha Bartlett’s Essay on the Philosophy of Medical Science was suggested to me several years ago by Dr. H. Tristram Engelhardt, Jr. Since that time it has been a pleasure to get to know the life and work of Elisha Bartlett. I am pleased to be completing this book in the bicentennial year of Bartlett’s birth. Bartlett was born in 1804 in Smithfield, Rhode Island, less than twenty-five miles from Worcester, Massachusetts, my present home—a short journey even in Bartlett’s day. I have been able to walk at some of the sites to which Bartlett continually returned during his life. Visiting Bartlett’s grave in the Slatersville cemetery has been an inspiration for the preparation of this book. Proximity to several institutions with rich holdings in Bartlett’s works and in nineteenth-century American history of medicine greatly facilitated my research. First, though, I want to acknowledge the College of the Holy Cross for supporting my sabbatical leave for the academic year 2003-2004. The American Antiquarian Society, in Worcester, Massachusetts, was generous in giving me access to its remarkable resources. I was able to find many of Bartlett’s published works and other nineteenth-century medical literature there, and the entire library staff provided quick and able research assistance.