In 1968, Josef Koudelka was thirty years old and although he had spent six years photographing gypsies and theatre, he had never covered a news event. During the Prague Spring, on the night of August 21, the city was invaded by Warsaw Pact tanks. Koudelka had returned just the day before from Romania, where he had been following gypsies. He took a series of photographs of the events in Prague and managed to have them smuggled out of the country. They reached New York and a year later the reportage was distributed by Magnum Photos. To avoid reprisals, the images were credited to an unknown Czech photographer - which did not stop Koudelka from winning the Robert Capa Award anonymously. However, it was not until sixteen years later, once the threats to his family had ceased and after the death of his father, that the photographer publicly acknowledged authorship. Forty years on, almost 250 of these searing photographs - most of them published here for the first time - have been selected by Koudelka from his extensive archive.