Here are the key dates in the wealthy Spanish region's independence drive.
2006
March 30: 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".
July 31: Prime Minister Mariano Rajoy's conservative Popular Party (PP), which has only marginal support in Catalonia, appeals the autonomy charter, accusing it of "privileging" Catalonia.
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2010
June 28: The Constitutional Court strikes down parts of the 2006 autonomy charter in response to the PP's appeal. 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.
July 10: Hundreds of thousands of people protest in Barcelona, the capital of Catalonia, chanting "We are a nation, we decide".
2012
September 11: 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.
September 20: 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.
November 26: Mas's centre-right CiU alliance wins the snap election overall but fails to secure an absolute majority in the regional parliament.
2013
September 11: Hundreds of thousands of Catalans join hands to form a human chain stretching more than 400 kilometres (250 miles) along the Mediterranean coast to push for independence.
2014
November 9: Catalonia defies Madrid and presses ahead with a symbolic vote on independence. Turnout is just 37 percent, but more than 80 percent -- 1.8 million people -- vote in favour of independence.
2015
September 27: The pro-independence Together For Yes alliance secures 62 seats in the regional assembly and the radical leftwing separatist group CUP wins 10, giving them an absolute majority.
But the separatist block falls short of winning a majority in the election, which is portrayed as a proxy vote on independence, capturing just 47.8 percent of the ballot.
November 9: All 72 pro-independence lawmakers in the Catalan parliament vote for a resolution that kicks off the process to secede from Spain. The resolution is later struck down by the Constitutional Court.
2016
January 10: Longtime separatist Carles Puigdemont becomes president of Catalonia.
2017
June 9: Puigdemont announces a referendum on independence to be held on October 1, 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.
July 3: 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".
September 6: Catalonia's regional parliament approves a law allowing the referendum and the regional government signs a decree officially calling the vote.
September 7: The Constitutional Court temporarily suspends the referendum following a legal challenge from Madrid but the Catalan government vows to push ahead.
September 13: Spanish prosecutors order police to stop the referendum by seizing ballots, ballot boxes, campaign posters and other material needed to stage the vote.
September 20: Police arrest 14 Catalan government officials suspected of organising the referendum and announce they have seized nearly 10 million ballots destined for the vote. Thousands protest against the police crackdown in Barcelona.
September 21: Catalan vice president Oriol Junqueras admits that plans to hold the referendum have been dealt a blow by the police crackdown.