While collecting materials some years ago for a history of the American hospital, I became increasingly interested in Florence Nightingale – one of the few individuals who exerted a peculiar and indispensable influence on that history. At first that influence seemed as difficult to understand as it was undeniable; her ideas were typical of the accepted wisdom of her generation, but were anachronistic by the 1880s and 1890s. An explanation seemed in order. And that explanation, I became convinced, lay in her ability to invoke a language of shared moral and conceptual reference, to articulate a world-view that at once explained the hospital's present evils and demanded their reform. It was in some ways her power as rhetorician as much as her social position and skill in bureaucratic infighting that explained Nightingale's enduring influence in nursing and hospital reform. But her ways of thinking about the world are very different from those we have come to accept in the twentieth century. As in understanding traditional therapeutics, understanding Nightingale's social impact means taking ideas seriously, no matter how alien and even inconsistent they may seem (or in her case how transparently they express a seemingly self-serving and hegemonic vision of social control). It means seeing their ultimate consistency, their ability to function as an explanatory, monitory, and hortatory system. Only then can a historian begin to appreciate her ability to mobilize the sentiments of so many of her contemporaries.