It may not occur to those who observe casually, and perhaps carelessly, the phenomenon of crime to what an extent it depends on, and can be explained by, strictly social conditions. What is summarized by criminologists under the title of '_l'hygiène préventive_' comprises all those social and political reforms which make up the 'Social Programme,' which is engaging the attention of our statesmen to-day. Better housing and lighting, the control of the Liquor Traffic, cheap food, fair wages, insurance, even village Clubs, and Boy Scouts, in fact, all the special and political problems in vogue to-day--all react directly on the state of crime. The great War--terrible and hard school of experience though it has been--has given us the great object lesson of what new conditions of life, resulting notably from the control of the Liquor Trade and facility of employment, can effect. A century of legislation directed to the changes of the penal code, or the methods of punishment, would not effect what social legislation, induced by the War, and affecting the daily habit and living of the people, has revealed during the last five years,--the numbers coming to prison reduced 75 per cent! 71 per 100,000 committed to prison in 1918, as against 369 in 1913: the committals for Drunkenness reduced from 70,000 to 2,000: the almost complete disappearance of Vagrancy--a reduction from 24,000 to 1,200--the "_plaie sociale_"--the despair and the problem of the prison and social reformer. By recapitulating shortly in this Preface the history of punishment in its successive phases since the question of Prison Reform first began to occupy the minds of statesmen and philanthropists in the middle of the eighteenth century, I have endeavoured to make it clear to those who, in the future, will be responsible for the law and practice of Prisons, the direction in which progress lies. Given firm, thoughtful, humane administration in all that concerns the actual custody of all offenders of both sexes of the various categories, given a wise classification and treatment according to age, sex, and nature of the offence--the future lies in Preventive Science; on the one hand, medical science, strictly so-called, which shall, by diagnosis and therapeutics of the mental and physical state, _in early age before it is too late_, correct and restrain by suitable preventive means, institutional or otherwise, the tendency to anti-social conduct; and on the other, social or political science, which, by raising the standard of life among the masses, will re-constitute the '_milieu_' whence vice and misery spring. Let not the reproach again be made by an English historian that "England falls shamefully below the level of foreign countries" in this great matter. If foreign countries rightly admire the method, discipline, firmness, and impartiality of our penal system, let them also recognize that we are not behindhand in what Preventive Science has to teach in the domain of medicine,