The International Day Against Homophobia, Transphobia and Biphobia was created in 2004 to draw the attention to the violence and discrimination experienced by lesbian, gay, bisexuals, transgender, intersex people and all other people with diverse sexual orientations, gender identities or expressions, and sex characteristics.

The date of May 17th was specifically chosen to commemorate the World Health Organization’s decision in 1990 to declassify homosexuality as a mental disorder.

For more info: https://may17.org/about/