There can be no doubt whatever in the mind of any student of the evolution of "civic conscience" that the prominence now being given to the subject of prostitution is one of the most promising signs of our day. It is inevitable in the first uncovering of what has been hidden for many generations that this prominence should be marred by much that is to be regretted, by much wild hysteria, and much morbid dwelling on erstwhile forbidden topics. But in the main the knowledge by the people at large of the cess-pools that lie below our civilization is the only starting-point from which to set about the draining and cleaning up of these cess-pools. As Dr. Flexner points out repeatedly in this volume, it is public opinion, and in the last analysis, that only, which determines the fate of prostitution in any given city. Even the most stringent laws are of comparatively little service when unsupported by an intelligent and watchful interest on the part of the people at large. And on what can an intelligent interest be founded except on knowledge? The voices raised in protest--the voice of Agnes Repplier, for instance--belong surely to the protected "leisure class"--the class which sees no need for change since they have never known from personal experience that such problems exist. Yet it is safe to say that for the great majority of the world's population the question of prostitution and its attendent train of disease, misery, and degeneration is and has always been one of the most vital questions of life. A single calm, wise, scientific book, like this of Dr. Flexner's, given into the hands of our boys and girls of eighteen, would do quite as much good, and for many dispositions infinitely more, than a whole battery of moral lectures, warning vaguely against the "wickedness of human nature" and the "allurements of sin." Not that this book was written for boys and girls. Far from it. It was written for the serious student of the social evil by Dr. Flexner as representative of the Bureau of Social Hygiene of New York City. It is an unprejudiced, authoritative statement of the present condition of prostitution in the various countries of Europe, and is the result of an impartial and painstaking personal investigation which required two years of the time of an educational expert.