In 1910, New York City was bursting at the seams as more and more people crowded into a limited supply of housing in the tenement districts of Manhattan and the older areas of Brooklyn. With no outlet for its exploding population, and the burgeoning social problems created by the overwhelming congestion, New York faced a serious crisis which city and state leaders addressed with dramatic measures. In March 1913, public officials and officers of the two existing rapid transit networks shook hands to seal a deal for a greatly expanded subway system which would more than double the size of the two existing transit networks. At the time the largest and most expensive single municipal project ever attempted, the Dual System of Rapid Transit set the pattern of growth in New York City for decades to come, helped provide millions of families a better quality of life, and, in the words of Manhattan borough president George McAneny (1910-1913), "proved the city's physical salvation." It stands as that rare success story, an enormously complicated project undertaken against great odds which proved successful beyond all measure. It is published in conjunction with the History of the City of New York Project.