- Barack Obama is inaugurated as the 44th President of the United States, becoming the first African American president.
- Israel launches Operation Cast Lead, a 22-day military offensive in the Gaza Strip.
- The global financial crisis continues, with the unemployment rate in the United States reaching 8.5%, the highest level since 1983.
February
- Somali pirates hijack the Maersk Alabama, an American cargo ship, and hold its captain hostage.
- The world's first cloned monkey, Zhong Zhong, is born in China.
- Venezuela and Colombia restore diplomatic relations after a 10-year freeze.
March
- The International Criminal Court issues an arrest warrant for Sudan's President Omar al-Bashir for war crimes and crimes against humanity.
- North Korea launches a long-range missile, prompting international condemnation.
- The Eurozone's economy contracts by 2.5%, the largest quarterly contraction since the euro was introduced in 1999.
April
- The H1N1 swine flu pandemic begins, with cases reported in Mexico and the United States.
- The United States and Russia sign the New START Treaty, which reduces the number of nuclear warheads each country can deploy.
- The Large Hadron Collider, the world's largest and most powerful particle accelerator, begins operations at CERN in Switzerland.
May
- The Sri Lankan Civil War ends with the defeat of the Tamil Tigers by the Sri Lankan government.
- President Obama delivers a major speech on Islam in Cairo, calling for a new beginning between the United States and the Muslim world.
- The world's first 3D-printed car is unveiled in Detroit, Michigan.
June
- Iran's disputed presidential election sparks mass protests, which are met with a violent crackdown by the government.
- The G20 summit is held in Pittsburgh, Pennsylvania, and focuses on the global financial crisis and climate change.
- Michael Jackson, one of the world's most successful pop singers, dies at the age of 50.
July
- The United Nations Security Council passes Resolution 1929, imposing new sanctions on Iran over its nuclear program.
- The Tour de France ends with Spain's Alberto Contador winning his third title.
- The World Health Organization declares the H1N1 swine flu pandemic to be over.
August
- Typhoon Morakot makes landfall in Taiwan, causing widespread flooding and landslides and leaving hundreds dead.
- US Airways Flight 1549 crashes into the Hudson River in New York City, but all 155 people on board survive.
- South Africa hosts the 2010 FIFA World Cup, with Spain defeating the Netherlands in the final.
September
- In the United States, President Barack Obama signs the Affordable Care Act into law, which is commonly referred to as Obamacare.
- The European Union and Russia sign a partnership agreement, aimed at improving economic and political relations.
- The Large Hadron Collider at CERN discovers a new subatomic particle, which is later confirmed to be the Higgs boson.
October
- Chile is struck by a magnitude-8.8 earthquake, causing widespread damage and more than 500 deaths.
- The Nobel Prize in Literature is awarded to German writer Herta Müller.
- The United Nations Security Council passes Resolution 1973, authorizing military action to protect civilians in Libya.
November
- The United States withdraws its combat troops from Iraq, ending the nearly nine-year war.
- The Arab Spring begins, with protests against authoritarian regimes spreading across the Middle East and North Africa.
- The global financial crisis continues, with Europe's sovereign debt crisis deepening and the United States facing the threat of a double-dip recession.
December
- The United Nations Security Council passes Resolution 1975, imposing sanctions on North Korea for its nuclear tests.
- The United States Congress passes the Don't Ask, Don't Tell Repeal Act, which allows gay and lesbian people to serve openly in the American military.
- WikiLeaks begins releasing a large number of classified United States diplomatic cables, causing international embarrassment for the United States.