Pride Month occurs in June each year to commemorate the Stonewall Riots (also called the Stonewall Uprising) which began on June 28, 1969.
"The Stonewall Uprising was a tipping point for the Gay Liberation Movement in the United States. In the United States the last Sunday in June was initially celebrated as "Gay Pride Day," but the actual day was flexible. In major cities across the nation the "day" soon grew to encompass a month-long series of events. Today, celebrations include pride parades, picnics, parties, workshops, symposia and concerts, and LGBTQ Pride Month events attract millions of participants around the world. Memorials are held during this month for those members of the community who have been lost to hate crimes or HIV/AIDS. The purpose of the commemorative month is to recognize the impact that lesbian, gay, bisexual and transgender individuals have had on history locally, nationally, and internationally."
Source: The Library of Congress