Arriving in Philadelphia in 1793 as a refugee, and carrying a letter of introduction to President George Washington, Abbé Ouvière soon remade himself in the United States—only not as a priest, but as a physician and scientist. The timing was opportune, as the population of his French compatriots in the city swelled in 1792 to nearly 10% of Philadelphians and with them came the yellow fever epidemic. Though no longer known as Abbé Ouvière, the priest plunged into the struggle against the epidemic, now as Dr. Pascalis, treating patients with American luminary Benjamin Rush and embarking on a long and storied career as a pioneering figure in early American science and medicine. This chapter details Pascalis’ life in America, from 1793 until his death in 1832, focusing attention on the windows that his biography open onto the contours and functions of religion, race, slavery, and science in the revolutionary Atlantic world.