In 1949 Georgia O’Keeffe donated 1,600 photographs by Alfred Stieglitz to the National Gallery, Washington: the ‘Key Set’ that became the touchstone for the Gallery’s collection, now comprising 15,000 American and European photographs. This magnificent volume presents 290 of its finest examples, from Fox Talbot’s Leaf Study (1839/40) to Adam Fuss’s daguerreotype For Allegra (2012) and includes work by virtually every great photographer, along with essays on the evolution of the medium and some of its most important practitioners.