The founders of the International Day Against Homophobia, as it was originally known, established the IDAHO Committee to coordinate grass-roots actions in different countries, to promote the day and to lobby for official recognition on May 17. That date was chosen to commemorate the decision to remove homosexuality from the International Classification of Diseases of the World Health Organization (WHO) in 1990.
The day, as a concept, was conceived in 2004. A year-long campaign culminated in the first International Day Against Homophobia on May 17, 2005. 24,000 individuals as well as organizations such as the International Lesbian and Gay Association (ILGA), the International Gay and Lesbian Human Rights Commission (IGLHRC), the World Congress of LGBT Jews, and the Coalition of African Lesbians signed an appeal to support the "IDAHO initiative". Activities for the day took place in many countries, including the first LGBT events ever to take place in the Congo, China, and Bulgaria. The date of May 17 was specifically chosen to commemorate the World Health Organization’s decision in 1990 to declassify homosexuality as a mental disorder.
In 2009, transphobia was added to the name of the campaign, and activities that year focused primarily on transphobia (violence and discrimination against transgender people). A new petition was launched in cooperation with LGBT organizations in 2009, and it was supported by more than 300 NGOs from 75 countries, as well as three Nobel Prize winners (Elfriede Jelinek, Françoise Barré-Sinoussi, and Luc Montagnier). On the eve of May 17, 2009, France became the first country in the world to officially remove transgender issues from its list of mental illnesses.
Frenchman Louis-Georges Tin was founder of the day, and acted as its Committee Chairperson until his resignation in September 2013. He was succeeded by internationally renowned Venezuelan trans rights activist, lawyer and law professor Tamara Adrián, who became one of the first trans legislators in Latin America in 2015.
Louis-Georges Tin and two other Committee members started a hunger-strike in June 2012 to urge the French president Hollande to introduce a UN resolution decriminalising homosexuality.
In France, same-sex marriage has been legal since May 18, 2013, a decision announced on May 17.
Biphobia was added to the name of the campaign in 2015.
The Enforcement Act of Judicial Yuan Interpretation No. 748 that legalised same-sex marriage in Taiwan was passed on International Day Against Homophobia, Transphobia and Biphobia in 2019, with the law coming into effect on 24 May 2019.
Source: Wikipedia