With unfailing accuracy, he questioned some of the things he saw and didn't like, used his pen and was a pioneer in photo-journalism. Using his own photography to fully illustrate his documentaries to indict the slums and tenements of a New York City in the dawn of a new century.
In December, 1889, his account of the abysmal quality of city life, illustrated by photographs, appeared in Scribner's Magazine which created a great deal of interest and, so the following year, a full length version, "How the Other Half Lives" was published. The book was read by Theodore Roosevelt, the New York Police Commissioner, and he had the city police lodging houses, that were featured in the book closed down. Roosevelt was much moved by Riis's accounts and photographs of the deprivations suffered by those poor souls living in such turgid conditions, that as he rose up the political ladder to President of the United States, he contributed greatly to increasing the living standards of the ordinary working classes.