Catalonia, a region of 7.5 million people bordered by the Mediterranean and the Pyrenees, is about the size of Belgium, accounting for 6.3% of Spain's territory and 16% of its population.
Its thriving economy, buoyed by industry, research and tourism, generates one-fifth of the economic output of the eurozone's fourth-biggest economy.
But it is also one of Spain's most indebted regions with a debt mountain of €75.4 billion at the end of March, equivalent to 35.2% of its GDP.
Catalonia regularly taps into a credit line run by Spain's central government that provides extra cash to regional governments.
With its own regional parliament, Catalonia already enjoys significant powers over matters such as education, healthcare and welfare.
Spain's economic woes, coupled with resentment that the region pays billions of euro more in taxes than it receives from Madrid, have pushed secession from the fringes of Catalan politics to centre stage.
The regional government argues that an independent Catalonia would be richer and better able to protect its language and culture.
It had already defied Madrid in November 2014 by holding a symbolic independence vote where more than 80% - 1.8 million people - of voters chose independence, though turnout was just 37%.
The most recent poll commissioned by the regional government in July showed 41.1% in favour of seceding, and 49.4% against.
Authorities in Catalonia pushed ahead with a banned independence referendum at the weekend. Dozens of protesters were injured in clashes with police as the central government in Madrid vowed to halt a vote it has branded a "farce".
Here are the key dates in the wealthy Spanish region's independence drive:
30 March: Spain's parliament approves a new autonomy charter for Catalonia that increases the region's fiscal and judicial powers and describes it as a "nation".
31 July: The conservative Popular Party (PP), which has only marginal support in Catalonia, appeals against the autonomy charter, accusing it of "privileging" Catalonia.
28 June: The Constitutional Court strikes down parts of the 2006 charter. It rules that using the word "nation" to describe the region has "no legal value" and rejects the "preferential" use of the Catalan language in municipal services.
10 July: Hundreds of thousands of people protest in Barcelona, the capital of Catalonia, chanting: "We are a nation, we decide".
11 September: At the height of Spain's economic crisis, more than a million people protest in Barcelona on Catalonia's national day, demanding independence in what turns into an annual tradition.
20 September: Prime Minister Mariano Rajoy rejects Catalan president Artur Mas's call for greater tax-and-spend powers for the region. Five days later, Mas calls a snap regional election promising to hold a referendum on Catalonia's future.
26 November: Mas's centre-right CiU alliance wins the snap election overall but fails to secure an absolute majority in the regional parliament.
11 September: Hundreds of thousands of Catalans join hands to form a human chain stretching more than 400 kilometres along the Mediterranean coast to push for independence.
9 November: Catalonia defies Madrid and presses ahead with a symbolic vote on independence. More than 80% - 1.8 million people - vote in favour of independence, though turnout is just 37%.
27 September: The pro-independence Together For Yes alliance secures 62 seats in the regional assembly and the CUP, a left-wing separatist group, wins ten, giving the two groups an absolute majority.
But the separatist bloc falls short of winning a majority in the election, which is portrayed as a proxy vote on independence, capturing just 47.8% of the ballot.
9 November: All 72 pro-independence politicians in the Catalan parliament vote for a resolution that kicks off the process to secede from Spain. The resolution is later struck down by Spain's Constitutional Court.
10 January: Longtime separatist Carles Puigdemont becomes president of Catalonia.
9 June: Puigdemont announces a referendum on independence to be held on 1 October, which will ask voters: "Do you want Catalonia to be an independent country in the form of a republic?" Spain's central government says it will block the referendum.
3 July: Puigdemont dismisses a member of his regional government who raised doubts about the viability of the referendum. Three other members of his government whose support for the vote was in doubt also step down, as does the head of the regional Catalan police.
Rajoy accuses the Catalan government of harbouring "authoritarian delusions".
6 September: Catalonia's regional parliament approves a law allowing the referendum, and the regional government signs a decree officially calling the vote.
7 September: The Constitutional Court suspends the referendum following a legal challenge from Madrid, but the Catalan government vows to push ahead.
13 September: Spanish prosecutors order police to stop the referendum by seizing ballots, ballot boxes, campaign posters and other material needed to stage the vote.
20 September: Police arrest 14 Catalan government officials suspected of organising the referendum and say they have seized nearly ten million ballots destined for the vote. Thousands protest in Barcelona against the police crackdown.
21 September: Catalan vice president Oriol Junqueras admits that plans to hold the referendum have been dealt a blow by the police crackdown.
29 September: The Catalan government says it has 2,315 polling stations ready for the referendum.
30 September: Police say they have sealed off over half of the polling stations.
1 October: Spanish riot police fire rubber bullets and force their way into Catalonia polling stations held by activists as thousands vote in the banned independence referendum. Regional authorities say that more than 800 people required medical attention after the crackdown by riot police.