Alvarado v Alvarado: Costa Rica's election explained
Costa Ricans have two choices in the presidential elections on Sunday: Alvarado or Alvarado.
Conservative evangelical Fabricio Alvarado is running against centre-left Carlos Alvarado, who is no relation.
The candidates have been neck-and-neck throughout the campaign, which has been dominated by debate over legalising same-sex marriage.
Here is what you need to know about the two candidates and the election.
- Costa Rica country profile
- Costa Rica election goes into runoff
- 'Don't be fooled' - busting fake news in Costa Rica
Why is Costa Rica voting?
Costa Rica has a presidential election every four years.
The current president, Luis Guillermo Solís of the centre-left Citizens' Action Party (PAC), is banned under law from running for a second consecutive term.
In February's first round, no candidate won more than 40% of the vote, which means the two best-performing candidates went through to a head-to-head second round.
Fabricio Alvarado won 24.8% of the vote in February, while Carlos Alvarado gained 21.8%.
The novelist v the preacher
Carlos Alvarado Quesada, 38, is the PAC candidate. He was the minister of labour under the former administration.
A graduate of the University of Costa Rica and the University of Sussex, Mr Alvarado Quesada is also a novelist and a former journalist.
He is running on a progressive platform under the slogan "Elijo el futuro" (I choose the future).
His opponent is Fabricio Alvarado Muñoz. The pair have sharply different views.
Mr Alvarado Muñoz, 43, is standing for the conservative National Restoration Party (PRN).
He is a journalist, devout Christian, evangelical preacher, and a singer of Christian music - he wrote the evangelical song, Tu amor es todo (Your love is everything).
What divides them?
There have been a number of key issues, including fears about the national deficit and the country's murder rate jumping to its highest-ever level last year.
But the core divide between the two Alvarados is same-sex marriage.
In January, the Inter-American Human Rights Court ruled same-sex marriages should be recognised - a decision applying to all signatory nations of the American Convention on Human Rights.
Mr Alvarado Muñoz is strongly opposed to the measure. He has vowed to fight it, railing against the "secular state" as well as "gender ideology".
Mr Alvarado Quesada, however, backs the ruling. He has accused his opponent of homophobia.
Who's going to win?
The two are neck and neck, with one poll from 22 March showing 43% backing Mr Alvarado Muñoz and 42% supporting Mr Alvarado Quesada.
This could be the closest vote in Costa Rica for decades. Polls open at 06:00 local time (12:00 GMT) and a winner is not expected to be announced until Monday at the earliest.