Yogini Ekadasi is observed today, 14/15 June 2012. As it begins in the morning on 14th June, Smartha people observe it as Smartha Ekadasi. Bhagvat (Vaishnava) Ekadasi is on June 15, 2012.
It falls in Krishna Paksha of Ashad month in North Indian Hindi calendars whereas it is Krishna Paksha Ekadashi in Jyeshta month in Telugu, Kannada, Marathi, and Gujarati calendars. Ekadashi begins on 14 June at 8.40 am and ends on 15 June 2012 at 11.08 am.
Yogini Ekadasi Vratha katha is mentioned in the Brahma vaivarta Purana. It is associated with the legend of Hemamali, a servant at Kubera, who neglects his duty due to his attraction towards wife.
You can read the full story of Yogini Ekadasi vrat katha here..