On Sunday, Colombians will vote on the newly signed peace agreement between the FARC guerrillas and the government of Colombia. The peace accord is an opportunity to end the longest-running conflict in Latin America. The conflict began in 1964. An estimated 220,000 people have been killed and millions more displaced.

The accord was signed this week between the government of Colombia and the FARC guerrillas and is now being submitted to the people for approval through a referendum.  The vote is the final, crucial step in ratifying this peace agreement. Here’s what you need to know.

Q: What exactly are people voting on?

When Colombians vote on Sunday, they will read on their ballots this single sentence: “Do you support the final accord to end the conflict and build a stable and lasting peace?”  They will then vote a simple “yes” or “no.”

The accord is composed of five elements, including disarmament and demobilization of the FARC, justice for victims of violence, cutting guerrilla ties to the drug trade, rural development and political participation for the FARC.  Some of these are widely popular, but others are deeply controversial.

Opposition forces have campaigned for separate elements of the deal to be up for a vote. Multiple ballot measures are far more difficult to pass, however. In 1998, Guatemala’s four votes on its peace accord failed in large part for this reason. The “yes” or “no” measure may increase the referendum’s chances of passing because of voters who support peace but not all of the accord’s provisions.

Q: Why is there even a need for this vote? Isn’t the signing enough?

This vote is the fulfillment of President Juan Manuel Santos’s promise at the outset of negotiations to allow voters an opportunity to accept or reject the results. That promise was made to bolster public support for a sequestered peace negotiation, in contrast with the open talks conducted by former president Andrés Pastrana from 1999 through 2002.

The referendum may therefore legitimize an agreement reached by elites. It may also erode the legitimacy of those who oppose it.

Q: Why would people oppose this deal? Doesn’t everyone want peace?

Many Colombians, who were the victims of violence and intimidation during the long war, object to making peace with the FARC. Colombians call the compromises in the peace accord “toad swallowing.” There are two toads that are particularly hard to choke down.

The first is the “amnesty” for former FARC guerrillas. For most crimes, if guerrillas and paramilitaries admit their crimes, they can avoid prosecution and jail.

The second is the power-sharing provisions, which hold a small number of seats for unelected FARC representatives in Colombia’s legislature for two years. This is done so that the former combatants will have a voice in the proceedings while the legislature makes decisions on the implementation of the accord.

A leading opponent is former president Álvaro Uribe, who was dedicated to defeating the FARC during his presidency (2002 to 2010). Uribe currently leads the conservative Democratic Center party. The former president and his party opposed the peace talks and are now campaigning against the referendum. Uribe enjoys a great deal of public support.

In contrast, President Santos’s approval ratings fell this year to around 20 percent. In urban centers, where voter turnout is higher, his numbers are even lower. Uribe has sought to make the vote on the peace accord a referendum on Santos.

Q: What will happen if the measure passes? What will happen if it fails?

The work of implementing the accord will start immediately. Colombia’s legislature will need to pass an amnesty law. FARC members will be required to report to “concentration zones” within five days of the referendum to participate in a United Nations-monitored, six-month demobilization and disarmament process. The amnesty law should be in place before disarmament begins.

The government will also need to quickly legalize and establish the truth and reconciliation and parallel justice structures outlined in the accord. There are also promises for investments in rural development and the reintegration of combatants.

Challenges to peace would remain, including the continuation of conflict with the ELN, another rebel group. The vacuum that the FARC leaves in the drug trade in rural areas is also anticipated to be a challenge for peace and stability.

The government’s chief negotiator has indicated that if the referendum is rejected, the peace accord would most likely not be implemented or renegotiated. If it fails at the polls, Sunday’s vote could freeze peacemaking for years to come. A rejection could also end the cease-fire put in place over the summer, returning the two sides to conflict.

Q: What do current polls suggest?

In early August, before the full plan was announced, support for the deal was around 40 percent. More recent polling indicates increasing support for the agreement. Polls from last week, before the official signing of the agreement, showed 65 percent support.

Moreover, the referendum requires a lower-than-usual level of turnout to pass. The last national referendum held in Colombia was in 2003, when 15 constitutional amendments were on the ballot and 14 failed to garner the necessary 25 percent turnout. This time, only 13 percent of registered Colombians must vote to validate the result.

Colombians are not necessarily happy with all of the accord’s provisions or with President Santos. However, if the choice is between an imperfect peace and a return to conflict, voters seem likely to opt for peace.

Katy Collin has a PhD in international relations from American University, School of International Service. Her research focuses on the use of referendums in peace processes.