Colombian voters were asked a simple question:
"Do you support the final agreement to end the conflict and construct a stable and enduring peace?"
Major polls had indicated resounding approval, but a shocking "no" result in the referendum has left the country, and its politicians, in a state of disbelief.
By a narrow margin, Colombians rejected a deal struck between President Juan Manuel Santos and the leaders of the Revolutionary Armed Forces of Colombia, or FARC.
Some "no" voters, who had endured years of killings and kidnappings by FARC rebels, viewed the deal as too lenient.
It would have given many fighters the chance to start living as normal civilians, kept out of jail, and given rebel leaders the chance to receive reduced sentences for war crimes.
The government's Chief Peace Negotiator, Humberto de la Calle, has resigned from his post in the aftermath, but he says not all hope is lost.
"Peace has not been defeated. And, actually, spokespeople for the Democratic Centre have said that, while they have issues with certain parts of the accord, the hope for peace is universal and unanimous. As I've always said, I profoundly respect the opinions against it."
The government and rebel representatives are now set to return to the negotiating table.
A new peace accord seems to depend on whether FARC representatives could accept some tougher sanctions against them.
Both parties have promised to maintain a ceasefire and keep working together, despite what could be another lengthy and complicated process.
FARC leader Rodrigo Londono says the intention is to stop the fighting.
"We reaffirm before Colombia and the world that guerilla fronts throughout the country will remain in bilateral and definite ceasefire as a necessary measure of relief to victims of the conflict and as respect for what was agreed with the national government."
Latin America's longest conflict has killed 220,000 people, displaced millions and brought atrocities on all sides.
The deal would have led to implementing a timetable to end the FARC insurgency within months, with the rebels agreeing to immediately abandon their camps throughout the country.
The rejection of the deal is a major political setback for President Santos, even though he holds a majority in congress and has it for his two remaining years in office.
Colombian senate president Mauricio Lizcano says the President has his full support.
"We support President Juan Manuel Santos in his effort to reach peace. We count on the desire of all Colombians, with the majorities in Congress and we know that the President maintains his legal and constitutional powers to achieve peace. In that matter, we support the decision to form a large and constitutional commission that will open a national dialogue with all the 'no' branches. We hope this commission has set timings and concrete results."
Negotiators have now been sent back to Havana, where they worked out the peace deal over almost four years, to discuss the crucial next steps.
