It's been a devastating war, with more than five decades of battle between the Revolutionary Armed Forces of Colombia (known by the Spanish acronym FARC) and the country's government.
It began in 1964, after the success of the Cuban revolution, with the rebels wanting to forcibly redistribute wealth.
In the more than 50 years since then, the armed group has seized territory, attacked government forces and interfered with political life through high-profile kidnappings. The rebels hijacked a commercial airliner to kidnap a senator in 2002, one of at least three passenger plane hijackings in the early part of the century. One of the group's most notorious feats was the capture of presidential candidate Ingrid Betancourt in 2002, who was held deep in the jungle for six years before she was rescued in a Colombian military operation.
FARC also turned to the drug trade, making millions from trafficking in cocaine. It was designated a terrorist group by the United States and the European Union.
The rebels forced children to become soldiers, training them as guerrillas to lay mines and fight.
As the decades passed, thousands upon thousands of people were killed. Up to 220,000 died in the insurgency and as many as 5 million people were displaced -- more than 1 out of every 10 Colombians.
The long, bumpy road to a peace deal
There have been sporadic attempts at peace since the 1980s.
A ceasefire brokered in 1984 included the release of a number of imprisoned guerrilla fighters. That truce ended in 1990 when several thousand former FARC members were killed.
Another attempt fell apart in 2002. Then-President Andres Pastrana ceded an area the size of Switzerland to the guerrilla group but ended negotiations after rebels launched a series of attacks across the country in an apparent bid to strengthen their position.
Talks about talks began again in August 2012 and the two sides met in Havana the following November. Cuban President Raul Castro presided over the negotiations that went on (and off and on) for four years before a ceasefire deal was signed this June
That was another step on the way to the full peace deal, signed Wednesday by President Juan Manuel Santos and rebel leaders.
The deal needs to be approved by a majority of Colombian citizens and a referendum has been set for October 2.
The plan is that FARC rebels will lay down their arms and leave their jungle strongholds.