The book focuses on the creation and use of power in New York local and state politics, as witnessed through Moses's use of unelected positions to design and implement dozens of highways and bridges, sometimes at great cost to the communities he nominally served.

[2] The Power Broker describes Robert Moses's strong-willed grandmother and mother before detailing his childhood in Connecticut, studies at Yale and the University of Oxford, and early career promoting progressive reform of New York City's corrupt civil service system.

Though Moses served in many of his public jobs without compensation (except for New York City Parks Commissioner), he lived lavishly and enabled similar lifestyles for his allies.

The book is 1,336 pages long (only two-thirds of the original manuscript), and provides documentation for its assertions in most instances, which Moses and his supporters attempted to refute.

'"[4] He found that despite Moses's illustrious career, no biography had been written, save the highly flattering and propagandistic Builder for Democracy in 1952.

[5] So he decided to undertake the task himself, beginning the seven-year process of hundreds of interviews meticulously documented as well as extensive original archival research, listed in the notes on sources in an appendix.

Ina, his wife and research assistant, sold the family home on Long Island and moved the Caros to an apartment in the Bronx where she had taken a teaching job, so that her husband could continue.

On June 12, 1975, The New York Chapter of the American Institute of Architects conferred a "Special Citation upon Robert Caro ... for reminding us once again, that ends and means are inseparable."

David Klatell, former interim dean of the Columbia University Graduate School of Journalism, recommended the book to new students to familiarize themselves with New York City and the techniques of investigative reporting.

Moses put out a 23-page typed statement challenging some of its assertions (for instance, he claimed he never used the anti-Italian slurs the book attributes to him about Fiorello La Guardia).

In 2017, David W. Dunlap described The Power Broker as "the book that still must be read – 43 years after it was published – to understand how New York really works.

[18] In the book Caro claims Moses built overpasses crossing his Long Island Parkways low in height to keep buses from transporting those without private automobiles (i.e. lower class, disproportionately non-white citizens) to the beaches and parks he developed as president of the Long Island State Park Commission.

German professor of sociology Bernward Joerges pointed out in 1999 that "Moses did nothing different on Long Island from any parks commissioner in the country" in designing bridges too low for buses to pass under.

Cornell city planning professor Thomas Campanella, in turn, measured the overpasses and found that they were "substantially lower on the Moses parkway" than elsewhere.