About 8 million Europeans live and work in EU countries other than their own, exercising one of their fundamental rights as EU citizens. But it's not always easy.
To curb sham marriages and other abuses of EU residence rights, some countries have set conditions on permits that have been found to violate EU law.
Amid complaints that the law is confusing, the commission recently published guidelines clarifying residence rights.
Some of the most common violations concern people from outside the EU who, through marriage to Europeans, also have the right to live and move freely in the EU.
Until recently, many countries required non-EU spouses to have residence rights in another EU state before they could get a permit in the new one. That made it easier for countries to deport spouses suspected of marrying EU citizens for the sole purpose of immigrating to the EU. But in a landmark ruling last year, the European Court of Justice found that the requirement violated the spouses' rights.
There have also been complaints that some countries require EU citizens to submit unnecessary documents when they apply for residence.
The new guidelines assert that EU countries can require non-EU spouses to have a visa. But they also say national authorities must provide spouses with a visa. Union countries can investigate suspected sham marriages, but based on a well-defined set of criteria. And they should make sure they consider all the circumstances in each case.
People can be deported if they present a threat to the country's "fundamental interests." Free movement can also be restricted on the grounds of public security.
Last year the EU reviewed compliance with the 2004 directive on free movement and found that many national laws transposing the law were deeply flawed. Not one country had managed to transpose the EU law fully, effectively and accurately.
Free movement in the EU - a fundamental right