June 21 was declared as the International Day of Yoga by the United Nations General Assembly on December 11, 2014. Yoga, a 6,000+-year-old physical, mental and spiritual practice having its origin in India, aims to transform the body and the mind.

The declaration of this day came after the call for the adoption of 21 June as International Day of Yoga by PM Narendra Modi during his address to UN General Assembly on September 27, 2014.

Source: https://en.wikipedia.org/wiki/International_Yoga_Day