Catalan MPs are voting on whether to seek the right to hold a referendum on independence from Spain.
The EU will be watching closely as Belgium's Dutch speakers gear up to push for greater autonomy in May elections, and Scotland prepares to hold its own referendum on breaking away from Britain in the autumn.
The vote is a milestone in years of mass protests by Catalans, who are fiercely proud of their distinct culture and language, demanding the right to decide whether they want to secede.
As MPs debated at the Catalan parliament in Barcelona before the vote, about 150 Catalans outside waved independence flags. A smaller group unfurled Spanish flags before the debate began, yelling "Catalonia is Spain!"
But the vote is also largely a symbolic one. Catalonia can ask Spain for permission to hold an independence vote all it wants; Madrid still has the power to say "no" - and it almost certainly will.
Prime Minister Mariano Rajoy has repeatedly said he won't allow a Catalonia secession referendum because Spain's 1978 constitution doesn't envision anything but a unified Spanish state, and mandates that referendums affecting Spain must be held nationally and not regionally.
He has an absolute majority in parliament that assures he will prevail, and the main opposition Socialist party also opposes a referendum vote.
Still, the vote, expected to win easily, could fan the flames of an already impassioned independence drive, especially if it gains the two-thirds majority that supporters are hoping for. A strong separatist message may also inspire independence movements elsewhere in the European Union at a time when European unity has been rocked by economic crisis.