1493 - Voyager Christopher Columbus claims Puerto Rico for Spain.
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 military vehicles, Puerto Rico
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.