The withdrawal of around 600 British troops from Bosnia-Hercegovina is due to begin as the role of international forces in the country is scaled down.
British troops had been supporting the Dayton Peace Accord
UK soldiers had been targeting war criminals' support networks and reducing illegal weapons ownership. The country itself is now largely stable.
Most of the returning soldiers are Welsh Guards. A small number of staff officers will remain in Sarajevo.
International forces are being reduced from 6,000 to 2,500 troops.
Brigadier Chris Murray, the overall commander of the British troops in Bosnia, said: "A safe and secure environment here in Bosnia has been achieved.
"Now that doesn't mean for a moment that this country is fixed, it isn't. There are still some dangerous fault lines here in this nation."
He added: "There are very serious ethnic problems in this nation, but they don't need to be underpinned by so many soldiers."
A series of commemorative events are to be held to honour the 55 British personnel who died and the thousands who served there since the UK first sent troops in 1992.
Although the EU peacekeeping force Eufor is being reduced, the international community overseeing the 1995 Dayton Peace Accord said it was retaining the office of the High Representative until June 2008.
It said the reforms it wanted had not yet been fully implemented.
The government has rejected claims that the move had anything to do with military commitments in Afghanistan.
Around 250,000 people died in the inter-ethnic war of 1992-95.
Initially British troops served with the United Nations, and then under Nato command until Eufor took responsibility for safeguarding peace in 2004.