Magnum Photos is an international photographic cooperative. It has offices in New York, Paris, London and Tokyo. Its owner-members are all photographers. It was founded in 1947 on an idea by Robert Capa. Robert was a photo journalist with extensive war experience. It’s other founding members included David “Chim” Seymour, Henri Cartier-Bresson, George Rodger and William Vandivert. You can see biographies and examples of their work at the official “Magnum Photos” web page.
The original plan was for Rodger to cover Africa and the Middle East; Cartier-Bresson to cover south and east Asia; Seymour and William Vandivert to cover Europe and the United States, respectively; and Capa to be free to follow his curiosity. As a result the agency has provided iconic images that span many of the twentieth centuries major conflicts. You have probablly seen many of the images.
Wikipedia lists 112 known members of which 28 have died, 18 have withdrawn and no one has ever been expelled. The only Australian member is Trent Parke.
According to co-founder Henri Cartier-Bresson,
“Magnum is a community of thought, a shared human quality, a curiosity about what is going on in the world, a respect for what is going on and a desire to transcribe it visually.”