By Pam O'Toole
BBC regional analyst
There are an estimated 10m to 12m Roma scattered across Europe - mainly in the eastern and central states.
Some Roma refuse to comply with their hosts' social rules
They suffer high unemployment rates, large numbers of them live below the poverty line and their average lifespan is shorter than other Europeans.
International efforts are now underway to help redress discrimination that has pushed them from mainstream society.
Since the Roma arrived from India many centuries ago, European countries have often regarded them as a problem.
Some resolved the "problem" by assimilation, containment, exclusion - or even extermination.
The Nazis designated the Roma as undesirable racial elements and many were sent to the death camps.
After World War II, many Roma found themselves behind the Iron Curtain and were forcibly settled by the new Communist countries.
It wasn't until the 1990s that the rest of the world heard of them again, following a wave of discrimination and attacks against them in some of their new home states.
One town in the Czech Republic built a wall to separate a local community from its Roma neighbours. In Kosovo, many Roma were driven out by returning Kosovar Albanians who alleged they had collaborated with the Serbs.
Groups working with the Roma say they have always been unpopular with their host countries because they refuse to comply with the same social rules.
Their supporters say they are the victims of institutionalised racism and have been used as scapegoats for anything from unemployment to housing shortages.
In the late 1990s, hundreds of Roma applied for asylum in western European states, saying the barrage of human rights abuses and discrimination against them amounted to persecution.
Only a small number were granted asylum. Many western countries maintained that they were only discriminated against, rather than persecuted, and in some cases introduced visa regimes specifically designed to keep them out.