HBO has released a trailer for the soon-to-be released documentary which takes a look at the case to overturn Proposition 8, California's now-ended ban on gay marriage.

After California voters in 2008 approved Proposition 8, marriage equality activists held massive protests in California and Utah, home of the Mormon Church, which played a key role in its passage.

The following year, two plaintiff couples – Kristin Perry and Sandy Stier and Paul Katami and Jeff Zarillo – challenged the amendment's constitutionally. It was the first marriage case to aim for the Supreme Court.

The Case Against 8 takes a behind-the-scenes look at the people and politics that helped shape the case that brought down Proposition 8. (The trailer is embedded on this page. Visit our video library for more videos.)

The film opens in New York and Los Angeles on June 6, the first anniversary of the Supreme court landmark ruling in the case. The documentary will expand to selected cities June 13.

The Case Against 8, which won the Directing Prize for U.S. Documentary at the 2014 Sundance Film Festival, premiers Monday, June 23 on HBO.