World Yoga day preparations are well under way in India.

Sunday, June 21, 2015, marks the first International Yoga Day, which the government of Prime Minister Narendra Modi is marking with a massive outdoor New Delhi gathering.

There are no reliable estimates of how many people regularly practice yoga in India, though the number is certainly in the millions.

Yoga long ago went mainstream, with ancient practices melding with techniques that have changed and evolved as teachers have taken them back and forth between India and the West.