Timeline: Puerto Rico

A chronology of key events.

1493 - Voyager Christopher Columbus claims Puerto Rico for Spain.

San Juan: An important port and tourist destination

Founded in 1508 by Juan Ponce de Leon

Population: 433,000

1508 - Spanish settlement begins; Spanish explorer Juan Ponce de Leon arrives.

1898 - Under the Treaty of Paris, Puerto Rico is ceded by the Spanish to the US at the end of the Spanish-American War.

1900 - US Congress institutes civil government in Puerto Rico under the Foraker Act. US maintains strict control over island affairs, prompting demands for more local control.

1917 - Jones Act grants US citizenship to Puerto Ricans.

1946 - US appoints Jesus T Pinero as Puerto Rico's first governor.

1947 - Partial self-government granted, enabling Puerto Ricans to elect their own governor.

1948 - Munoz Marin elected as governor by popular vote. As leader of the Popular Democratic Party (PPD), he serves four terms.

1950 - October - President Truman signs the Puerto Rico Commonwealth Bill, paving the way for a Puerto Rican constitution. Nationalists oppose the new law and resort to violence. In November two US-based nationalists attempt to assassinate President Truman in Washington DC.

1951 - Puerto Ricans vote overwhelmingly in favour of US commonwealth status in a referendum.

1952 - 25 July - Puerto Rico's constitution is proclaimed, establishing a commonwealth with autonomy in internal affairs.

US Navy's use of its Vieques base sparked protests

2002: The Puerto Rican paradox

2003: Island marks US Navy's exit

1954 - Nationalists open fire in the US House of Representatives, injuring five congressmen.

1963 - World's largest radio telescope inaugurated at Arecibo Observatory.

1967 - Referendum on island's political status: 60% of voters back continued commonwealth status.

1985 - Landslide in Ponce kills 129 people.

1993 - Spanish and English declared as official languages.

Nearly 49% of voters back continued US commonwealth status.

1998 September - Hurricane George sweeps across the territory causing serious damage. President Clinton declares Puerto Rico a disaster zone.

1999 April - Off-target bombs kill a security guard on Vieques, an island which is home to a US Navy bombing range, triggering large-scale protests.

Grito de Lares flag, a symbol of nationalist aspirations

2000 November - PPD's Sila Calderon elected as first female governor.

2001 June - President George W Bush agrees to halt the use of the Vieques bombing range by May 2003.

2003 1 May - US Navy closes its bombing range on Vieques

2004 December - Ruling party's Anibal Acevedo Vila is confirmed as the territory's next governor after nearly two months of legal wrangling over a 0.2% margin of victory.

2005 July - Voters in a referendum back the idea of replacing the island's Senate and House of Representatives with a one-house legislature.

Rebel leader killed

2005 September - Fugitive pro-independence rebel leader Filiberto Ojeda Rios is killed in a shoot-out with US federal agents. The handling of the incident causes anger on the island.

2006 March - US Supreme Court rejects an appeal calling for Puerto Ricans to have the right to vote in US presidential elections.

2006 May - Budget shortfall leads to the closure of schools and many government agencies. Thousands of people take to the streets in protest.

2006 November - Puerto Rico adopts its first sales tax, aiming to address major budget deficits.

2008 March - Governor Acevedo Vila pleads not guilty to corruption charges in connection with alleged irregularities over the funding of election campaigns between 2000 and 2004.

2008 June - Mr Acevedo Vila calls on the UN to back Puerto Rico's right to self-determination.

2008 November - Luis Fortuno of the pro-statehood New Progressive Party wins gubernatorial election and is inaugurated in January.

2009 May - tens of thousands of workers march through San Juan in protest at possible job layoffs after Governor Fortuno announced a major programme of public spending cuts in March.

Former governor Anibal Acevedo Vila found not guilty on all counts in a corruption trial linked to allegations of raising and hiding thousands of dollars in illegal election campaign contributions.

2009 October - Whole neighbourhood near San Juan evacuated after an explosion at an oil refinery triggered a major fire. The blast was measured to a strength of a 2.8-magnitude earthquake.

2010 October - Dozens of Puerto Rican police are held on drugs charges following the biggest police graft probe in FBI history.

2011 June - President Barack Obama becomes first president since John F. Kennedy to make an official visit to Puerto Rico.

2011 December - Governor Fortuno gives go-ahead for August 2012 referendum to help decide island's political status.