This biography details the life and impact of Jacob Riis, a Danish immigrant who documented New York's impoverished areas through pioneering flash photography. His seminal work, "How the Other Half Lives," catalyzed social reform and supported Theodore Roosevelt's police reform efforts. Riis tackled issues like immigration, wealth disparity, and educational needs, though his advocacy was tainted by racial prejudices. He remained active, authoring further works and engaging in public lectures. The book includes a picture essay of Riis' photographs, along with 35 black-and-white illustrations, a chronology, further reading, and an index, providing a comprehensive view of his enduring legacy.