The anticipation was building even before the start of the five-day festival on Thursday, said Heidi Rosenau, a Lindy hop enthusiast and an administrator at the Frick Collection. “It began,” she said, “with a lesson taught by godlike Swedes” last weekend.

While dancers in places like California and Britain played important roles in the revival of the Lindy hop, dance historians say Swedes were essential.

“The thing about godlike, I’m not really sure,” said Catrine Ljunggren, a Swedish-born swing dancer and instructor. “But we were pretty much the first people who took it seriously again after the ’30s and ’40s.” So seriously that there is even a camp devoted solely to teaching the dance.

The organizers expect more than 2,000 dancers from 47 countries to attend the festival, which includes workshops and competitions. “It’s pretty international now,” said Donna Skiff, the director of the National Museum of Dance in Saratoga Springs, N.Y. “It’s a fun dance, and you don’t have to have real ballet training to do it. It means people without all that training can participate in dance, and people at all age levels. I’m amazed that the ones we’ve had here for performances, they’re young. They’re, like, teenagers. They dress the part. They look like that era.”