The Catalan government is expected to declare independence in the coming days. Here is a look at some of the issues surrounding the biggest political crisis to hit Spain in recent years:
How has the current situation come about?
Catalonia, a region in the north-east of Spain, has a population of some 7.5 million people, its own language and generates about a fifth of the country's wealth.
Catalans who want independence from Spain argue the region would be more prosperous governing itself.
In 2006 the region was given more devolved powers on things like healthcare and education but a move by Spain's Madrid-based Constitutional Court four years later to strike down some parts of the earlier agreement provoked anger among pro-independence Catalans.
What happened on Sunday?
An independence vote, deemed illegal by the Madrid government and the country's top court, was held after being backed by Catalan regional authorities.
The poll descended into violence when national police used force in an attempt to stop people voting, leaving hundreds injured.
How did the main players react?
Catalan government spokesman Jordi Turull said Spain had become "the shame of Europe" after scenes of police taking on voters were beamed around the world and splashed across the front pages.
Spanish prime minister Mariano Rajoy thanked police for acting with "firmness and serenity" as he insisted no independence vote had taken place and Spain's King Felipe VI accused Catalan authorities of deliberately bending the law with "irresponsible conduct".
Catalan officials said 90% of the 2.26 million people who took part in the vote backed independence. The region has 5.3 million registered voters.
What does the future hold?
Catalan authorities have said they are determined to press ahead with implementing the results of the vote.
Why have some of Spain's EU partners appeared keen to back Madrid?
Cynics might suggest domestic concerns may partly explain this.
For example, some of Mr Rajoy's clearest backing has come from French President Emmanuel Macron, whose country has faced low-level breakaway sentiment from Corsica and the Basque Country, which straddles both south-west France and north-west Spain.
There have also been separatist rumblings in northern Italy, Sardinia and Flanders in Belgium.