The first essay synthesizes the main findings of a collective biographical survey of key writers in the field of delinquency prevention between 1900 and 1930. During this time, belief in the possibility of delinquency prevention grew as never before among scholars, government officials, and lay civic reformers, substantially influencing responses to children's antisocial and illegal behavior by schools, courts, police, and mental health facilities. The authors, whose work is believed to embody the most significant strands of thought in the field, are Henry Goddard, William Healy, Lewis Terman, Ben Lindsey, Thomas Eliot, Miriam Van Waters, and Frederick Thrasher. Whereas Goddard, Terman, and Healy had little to say on the links between delinquency and urban community, Lindsey, Eliot, Van Waters, and Thrasher, each in very different ways, had a great deal to say. Future research in this area should center on the work of hundreds of anonymous civic leaders who spearheaded neighborhood campaigns in the 1920's and 1930's to combat juvenile crime. The second essay synthesizes the main findings of an inquiry into the emergence of State policy in delinquency prevention in the early 20th century. The focus was on California and selectively on Ohio. Examined were three institutional expressions of growing governmental interest in delinquency prevention: (1) attempts to revamp California's reformatory for boys at Whittier to rehabilitate delinquents more effectively than was done in the 19th century, (2) attempts to do the same in California's reformatory for girls at Ventura, and (3) the establishment in both California and Ohio of State-sponsored research bureaus to analyze the causes of delinquency and to recommend measures for prevention and treatment. A major finding of this study was that between the intention to implement delinquency prevention as a strictly scientific process and the reality of the daily routines of institutional life in California and Ohio fell a shadow that has darkened relationships among social and behavioral scientists, administrators, and elected public officials ever since. Footnotes accompany each essay.