From the nineteen-fifties until a few years before she died destitute in 2009, Vivian Maier took at least 150,000 pictures, mostly in Chicago, and showed them to nobody.

For decades, she supported herself as a nanny in the wealthy enclaves of the city. But her real work was roaming the streets with her camera (often with her young charges in tow), capturing images of sublime spontaneity, wit, and compositional savvy.

Maier’s covert work might have languished in obscurity if not for the chance acquisition, in 2007, of a cache of negatives, prints, contact sheets, and unprocessed rolls of film, all seized from a storage locker because she fell behind on the rent.

When John Maloof, a Chicago real-estate agent, bought the material, everything about Maier’s identity was a mystery except for her name. It was only when he ran across her death notice, two years later, that her story began to unfold.

Now Maier has earned her place alongside Diane Arbus, Robert Frank, Lee Friedlander, Lisette Model, Garry Winogrand, as a as a giant of American street photography.