Justin Brooks Atkinson was an American theatre critic. He worked for The New York Times from 1925 to 1960. In his obituary, the Times called him "the most important reviewer of his time."
I read this book many many years ago; it was one of the choice items in my collection of books about theater (when I had one). Brooks Atkinson was one of the most famous drama critics of his time (roughly, the 1930s thru 1960s). His terse, opinionated style is eminently readable even if his ideas about some plays (like Waiting for Godot) are way off the beam.
Anyway, this book is a chronicle of Broadway from its emergence as the center of American theater in the late 19th century through the time of its publication (about 1970). It's an excellent history, filled with great photos and insider stories, accounts of the creation of some of the most significant work in American drama, and lots of background about the business, the theaters, and the Broadway community.
I'm not sure that I can recall anything specific that I learned from this book, but I know that I enjoyed it and treasured having it.