The first festival ran from January 21 to 29, 1961. A handful of Cosquín residents, led by two local doctors, Reinaldo Wisner and Alejandro Guinder, wanted to put on a folklore show during the summer holidays to bring visitors to town. The response overwhelmed them. Musicians arrived from across the country, and almost overnight Cosquín became Argentina's largest annual folk event. From the second year, Radio Belgrano of Buenos Aires began broadcasting the Nine Moons live to a nationwide network, carrying the festival into homes across an enormous, far-flung country. After the third edition, the president decreed the last week of January National Folklore Week, with Cosquín as its capital.

In 1965, one of the most important moments in Argentine music happened almost in secret. Mercedes Sosa, then in her twenties, was on a list of artists barred from the official program for her open political sympathies. The organizers would not let her perform. So the beloved folk singer Jorge Cafrune did something quietly defiant: during his own set, he stopped and called her up to sing in his place. Sosa stepped to the microphone and performed "Canción del derrumbe indio," a lament for the conquest of the Americas' native peoples. The crowd would not let her go. A singer who had been forbidden a place left as a discovery, and went on to become the voice of a continent.

If Sosa is the festival's conscience, the guitarist and poet Atahualpa Yupanqui is its patron. He won the festival's first prize in 1967, and in 1972 the newly completed main stage was named in his honor; it stands today on Próspero Molina Square. Cosquín became the launching place for nearly every great name in Argentine folk - Mercedes Sosa herself, León Gieco, Víctor Heredia, Eduardo Falú, the harmony groups Los Chalchaleros and Los Fronterizos, the young Soledad Pastorutti. For decades, the master of ceremonies Julio Mahárbiz opened each season with a cry that became the festival's signature: "¡Aquí, Cosquín!" He borrowed the rolling style, he once said, from a famous football announcer of the day. Argentines who have never set foot in the town can still hear it. There is even a word for the festival's particular spell - the duende coscoíno, the Cosquín elf, the thing that keeps the peñas singing past the point of tiredness.

Cosquín's reach long ago outgrew its valley. The Organization of American States became a sponsor, recognizing the festival's place in the culture of the Americas, and Paris's Musée de l'Homme recorded its performances. Stuttgart named a stage "Cosquín"; since 1975 the Japanese town of Kawamata has held its own "Cosquín en Japón" each October. Back home, the festival is more than a competition. Its soul lives in the peñas - tents and riverside bonfires where musicians and revelers sing and dance until, as the saying goes, the candles burn out. A 2001 arena with a rotating stage now seats close to ten thousand. But the real Cosquín is still nine nights of strangers becoming a chorus under the summer moon.