"To take a photograph is to align the head, the eye and the heart," Henri Cartier-Bresson famously proclaimed. Five years after co-founding Magnum Photos, he published what is perhaps the most iconic book in photographic history. With that now familiar cover by contemporary Henri Matisse, The Decisive Moment, as it was called in English, defined the parameters of what it meant to be a photographer in the 20th century. Everything--the head, the eye, the heart, but also the frame, the light, the shapes--had to come together in one precarious, frozen fragment in time. The book's title in French, Images à la Sauvette, or "images on the run" provides insight into the vigilance with which Cartier-Bresson saw the world around him. To blink was to miss the photograph you sought.