Colombian President Alvaro Uribe has signed into law a controversial bill aimed at encouraging guerrilla and paramilitary groups to disarm.
The right-wing AUC are already in the process of disarming
In return, fighters are offered reduced prison sentences.
The Justice and Peace bill has been criticised as too lenient both nationally and internationally.
Mr Uribe has gone ahead with the law despite objections from the United Nations and groups including Amnesty international and Human Rights Watch.
The legislation was passed primarily to demobilise the right-wing paramilitaries known as AUC - the United Self-Defence Forces of Colombia.
People found guilty of massacres or crimes against humanity will face prison sentences of no more than eight years, to be served in special work farms.
Many others could walk away without punishment and might even benefit from a government subsidy for two years.
However, Mr Uribe is expected to struggle to find the funds needed to demobilise some 15,000 fighters, reports the BBC's Jeremy McDermott.
The president said the new law would not only apply to the AUC, but to all those guerrilla groups who commit to a peace process, EFE news agency said.
He also said that victims would be entitled to compensation.
In Colombia, Congresswoman Gina Parody said the law sent a clear message to Colombian society, namely that crime does pay.
The AUC says it is committed to demobilising all its fighters by the end of the year.
Several thousand of their militants have already laid down their arms.