Ireland is on the verge of becoming the first country in the world to support gay marriage by a popular vote when it holds a referendum on Friday. Here’s what you need to know.

What is the law now?

Gay couples have been able to be united in a civil ceremony, which is not the same as marriage, since 2011. Homosexuality was only decriminalized in 1993.

What will the people of Ireland vote for on Friday?

Voters will be asked to approve this addition to the Irish constitution: “Marriage may be contracted in accordance with law by two persons without distinction as to their sex.”

A Yes vote will endorse the Marriage Equality Bill 2015, which was passed by Irish lawmakers in March.

What do opinion polls suggest the result will be?

A survey of opinion polls by the Irish broadcaster RTE found that all polls suggested a victory for Yes, with predictions ranging from 53% to 69% in favor of the change. However the polls also suggested that the number of people moving from a Yes to a No position was increasing.

As pollsters appeared to get the recent U.K. election so wrong, no one is sure what the result could be.

But isn’t Ireland a socially conservative Catholic country that is beholden to the Catholic Church?

Attitudes have changed immensely in the past 30 years. The authority of the Catholic Church has been undermined by a litany of scandals from the abuse of children by priests to abusive regimes at church-run institutions such as schools and homes. The church wants to see a No vote, but an institution that protected abusive priests for decades no longer has the moral force it once had.

What does the Irish government think?

Irish Prime Minister Enda Kenny and former Irish President Mary McAleese have called for a Yes vote. The current President Michael Higgins as head of state is not expected to offer an opinion on political matters.

Does this vote affect Northern Ireland as well as the Republic of Ireland?

This vote only affects the Republic of Ireland. Gay marriage is legal in the U.K., except in Northern Ireland.

Who is against the gay-marriage amendment?

The Catholic Church is opposed to the amendment, and letters from bishops were read to congregations all over Ireland on Sunday. The church is supported by some conservative politicians and some polls suggest popular opposition to the amendment could be as high as 30%.

What do Irish celebrities think?

Very few people who are well known outside of Ireland have said they will vote No. The actor Colin Farrell has said he supports a Yes vote, as has actor Chris O’Dowd.

Singers Hozier and Glen Hansard, who wrote and starred in the film and Broadway musical Once, are also in the Yes camp.

But one of the most important supporters of a Yes campaign is Daniel O’Donnell, Ireland’s leading country and western singer, who is very popular in rural areas and among church-going women.

But what does Bono think?

Speaking in Vancouver, before the start of U2’s tour, he said he supported a Yes vote although he will not be voting:

“You can’t own it. Marriage is now an idea that transcends religion. It is owned by the people. They can decide. It is not a religious institution. As far as I know, Jesus wasn’t a married man and neither are most priests talking about it. It is not a religious idea.”

Correction: This article was amended on May 21 to show that Mary McAleese is the former Irish President and that gay marriage is not legal in Northern Ireland.

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