The Colombian Congress has approved a law setting up guidelines for peace talks between the government and left-wing guerrilla groups.
The so-called Legal Framework for Peace calls for soft sentences for rebels if they confess and compensate victims, and agree to lay down arms.
The move marks a shift from the policies of previous governments, which have refused to negotiate with rebels.
But critics say the legislation is too lenient.
Human rights groups as well as right-wing politicians - many close to former President Alvaro Uribe - say it would allow crimes to go unpunished.'Negotiated end'
The law, which has the backing of President Juan Manuel Santos, passed in the congress by 65 votes to three.
It applies to the Revolutionary Armed Forces of Colombia (Farc) and National Liberation Army (ELN), but does not include criminals involved with drug cartels or former paramilitary groups.
The Revolutionary Armed Forces of Colombia (Farc) has been weakened in recent years, but has stepped up attacks in recent months.
Lawmakers who voted in favour of the legislation say it was borne out of necessity.
"This is the price to pay for peace, we have to be upfront with people about it," Senator Hernan Andrade, a member of the governing "U" party, told Reuters news agency.
Correspondents say rebel leaders have given mixed signs that they are interested in talks, and it is not clear whether they will accept the conditions set out in the proposal.
But it is the most powerful sign that the current political class is willing to accept a negotiated end to the conflict, says the BBC's Arturo Wallace in Bogota.
That was unthinkable two years ago, he says, but the situation changed after Mr Santos came to power.
However, Mr Santos insists he will only act when he is sure the rebels mean business, our correspondent says.