The first International Yoga Day in 2015 saw people from all around the world participate. This led to a number of yoga-related world records being broken, such as the largest number of peopled in a yoga class (35,985) and the most number of nationalities represented in a single yoga class (84).
Assigning the date of June 21, which is the date of the summer solstice, is fitting. It is the day that Shiva is said to have first introduced yoga to the world through the Seven Sages (Saptarishi), earning him the title of Adiyogi ("first yogi"). In yogic tradition, this date is when the transition to Dakshinayan occurs -- a time when support for spiritual practices is deemed to be at its strongest.