It's the world's first national referendum on same-sex marriage.
The polls in the The Republic of Ireland opened on Friday morning and turnout is said to be higher than in previous public votes.
The electorate has turned out especially early in urban areas, with greater Dublin reporting 20% of votes cast before lunch. On the other hand, turnout is slow in the more rural areas, which is thought to benefit the 'Yes' vote.
Should the majority of the country say ‘Yes’ to the Marriage Equality Bill, it will be enshrined in the constitution and same-sex couples will be free to marry.
Irish people living the UK have flocked back to home to participate in the historic vote, with many tweeting under the hashtag #hometovote.
And the 'Yes' campaign is receiving widespread support from all around the world on the internet – from Stephen Fry to Sarah Silverman.
Here's a Q&A to help you understand what's going on.
Where did this referendum come from?
It’s been on the cards for four years now; it started when the Fine Gael-Labour coalition government came to power in 2011 and Eamon Gilmore, the Deputy Prime Minister, called gay rights “the civil rights issue of our generation”.
They set up a constitutional covenant which voted in favour of extended marriage rights; May 22nd was chosen as referendum day earlier this year.
Is a referendum necessary?
You may observe that the other 18 countries that have legalised gay marriage, like the UK for instance, have just changed the law (this doesn't apply in Northern Ireland though) – there was no need for a public vote.
But Ireland’s constitution is near-iron clad, with the public required to give amendments the rubber stamp before they come to be.
The constitution doesn't explicitly say that marriage can only be between and man and woman, but it’s sort of better-safe-than-sorry; that way they can avoid Supreme Court appeals.
What will they be asked?
The constitutional amendment is phrased as such: “Marriage may be contracted in accordance with law by two persons without distinction as to their sex.”
If they agree to that, they say yes. If not, no.
Inspirational quotes about LGBT rights
Inspirational quotes about LGBT rights
1/27 Caitlyn Jenner
"Why do people think it's OK to ask deeply personal questions when you're transgender?"
Reuters / Vanity Fair
2/27 Kanye West
"Look, I can be married to the most beautiful woman in the world, and I am. I can have the most beautiful little daughter in the world, and I have that. But I'm nothing if I can't be me. If I can't be true to myself, they don't mean anything," the rapper said about Jenner.
3/27 Stephen Fry
"Homosexuals are not interested in making other people homosexuals. Homophobes are interested in making other people homophobic."
4/27 Hillary Clinton
"Gay rights are human rights."
5/27 Anderson Cooper - Journalist and TV host
“The fact is, I'm gay, always have been, always will be, and I couldn’t be any more happy, comfortable with myself, and proud.”
6/27 Laverne Cox - Actress
'"We are not what other people say we are. We are who we know ourselves to be, and we are what we love."
7/27 PM David Cameron
"I am proud that we have made same-sex marriage happen. I am delighted that the love two people have for each other — and the commitment they want to make — can now be recognised as equal."
8/27 Kellie Maloney
"We don't have a choice. People think we wake up one morning, put a dress on and be a woman. I knew about it when I was very young but I was brought up in a male world and had responsibilities, I was frightened and I wanted to beat it. I didn't want to lose my friends. In the end I was so depressed and so desperate, I tried to commit suicide about three times."
9/27 Ellen DeGeneres - comedian and TV host
"To me beauty is about being comfortable in your own skin. It's about knowing and accepting who you are."
10/27 President Barack Obama
"Just to prohibit somebody who cares about another person, it just seems to me that's not what America's about. Usually, our constitutions expand liberties, they don't contract them."
11/27 Zac Efron - Actor
"To me, being gay was just another way that you can be."
12/27 Lance Bass - former NSYNC member
"The thing is, I'm not ashamed - that's the one thing I want to say. I don't think it's wrong, I;m not devastated going through this. I'm more liberated and happy."
Larry Busacca/Getty Images
13/27 Ed Miliband - former Labour leader
"Whether you're gay or straight, you should be able to signify your commitment, your love, with the term marriage."
14/27 Kate Bornstein - Author
"Gender is not sane. It's not sane to call a rainbow black and white."
15/27 Adam Levine - Maroon 5's singer
"Maybe we should make straight marriage illegal. It doesn't seem to have a very high success rate."
16/27 Tom Daley - Olympic diver
"I felt so alone and trapped in who I was... for people to be so supportive about it has been amazing."
17/27 Kurt Cobain - Former musician
"I'm not gay, although I wish I were just to piss off the homophobes."
18/27 Jay-Z - Rapper
"You choose to love whoever you love. It's no different than discriminating against blacks."
19/27 Brittney Griner - Basketball player
"I am a strong, black, lesbian woman. Every single time I say it, I feel so much better."
20/27 Daniel Radcliffe - Actor
"You don't have to be gay to be a supporter, you just have to be human."
21/27 Elle Page - Actress
"I am tired of hiding and I am tired of lying by omission... I suffered for years because I was scared to be out... I'm gay."
22/27 Michael Sam - NFL player
"I want to own my truth... No one else should tell my story but me."
23/27 Pink - singer
"I think the best day will be when we no longer talk about being gay or straight... It's not a gay wedding, it's just a wedding. It's not a gay marriage, it's just a marriage."
24/27 Jason Collins - former NFL player
"When I acknowledged my sexuality, I felt whole for the first time."
25/27 Ricky Martin - singer
"Acceptance has to come from within and this kind of truth gives me the power to conquer emotions I didn't even know existed."
26/27 Frank Ocean - Musician
"I believe that marriage isn't between a man and a woman; but between love and love."
27/27 Elton John
"So I am deeply saddened and shocked over the current legislation that is now in place against the LGBT community here in Russia. In my opinion, it is inhumane and it is isolating."
So, will the Irish people legalise gay marriage?
Well we’ll know the results the day after, but all opinion polls point towards a big win for the ‘Yes’ vote and legal gay marriage across Ireland.
A year ago there was an astonishing near-80 per cent in favour of legalising same-sex marriage, but it’s no longer quite as overwhelming. That said, the raft of opinion polls published in the last few days indicate that it’s still pretty straightforward.
An Irish Times/Ipsos poll said the ‘Yes’ vote stood at 58 per cent, whilst ‘No’ was at 25 per cent. Other surveys gave the ‘Yes’ vote 69, 63 and 53 per cent respectively. There’s been a significant uptick in the number of undecideds in the last few months.
Where does the government stand on the issue?
It seems as though everyone wants it to pass. Out of 226 members of parliament, only 5 have come out publicly against the amendment. It’s got cross-party support.
The Irish Prime Minister Enda Kenny backs ‘Yes’, as does former Irish President Mary McAleese.
Why is this such a big deal?
It’s a huge step for Ireland, one of the most Catholic countries in the world (around 80 per cent). The country only introduced civil partnership four years ago, and only decriminalised homosexuality in 1993.
Ireland, more than most countries, has referendums. But it’s been observed that this one, as opposed to the votes on divorce and abortion in the 1980s and 90s, has been far gentler.
Whether this will have a knock-on effect on other social policies is still up in the air.
Where does the Catholic Church stand in all this?
The Catholic Church itself is keeping largely quiet, though it obviously opposes the proposed amendment. The thing is, it doesn’t seem as though the Church could make-or-break this vote even if it tried.
Decades of child abuse scandals have tarnished the institution in the eyes of many of the Irish, and now only 35 per cent say the Church could or has influenced their vote on the matter. That may sound like a like, but it’s not for Ireland.
In its stead, Catholic community groups have taken the lead on the ‘No’ side of things.Reuse content