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1998 (MCMXCVIII)was a common year starting on Thursday of the Gregorian calendar, the 1998th year of the Common Era (CE) and Anno Domini (AD) designations, the 998th year of the 2nd millennium, the 98th year of the 20th century, and the 9th year of the 1990s decade.
1998 was designated as the International Year of the Ocean.
- May 11
- India conducts three underground nuclear tests in Pokhran, including one thermonuclear device.
- The first euro coins are minted in Pessac, France. Because the final specifications for the coins were not finished in 1998, they will have to be melted and minted again in 1999.
- May 13–14 – Riots directed against Chinese Indonesians break out in Indonesia, killing around 1,000 people.
- May 19
- May 21 – Suharto (elected 1967) resigns, after 32 years as President of Indonesia and his 7th consecutive re-election by the Indonesian Parliament (MPR). Suharto's hand-picked Vice President, B. J. Habibie, becomes Indonesia's third president.
- May 28 – Nuclear testing: In response to a series of Indian nuclear tests, Pakistan explodes five nuclear devices of its own in the Chaghai hills of Baluchistan, codenamed Chagai-I, prompting the United States, Japan and other nations to impose economic sanctions. Pakistan celebrates Youm-e-Takbir annually.
- May 30
: Nairobi Embassy bombing.
- August 4 – The Second Congo War begins; 5.4 million people die before it ends in 2003, making it the bloodiest war, to date, since World War II.
- August 7
- Yangtze River Floods: in China the Yangtze river breaks through the main bank; before this, from August 1–5, peripheral levees collapsed consecutively in Jiayu County Baizhou Bay. The death toll exceeds 12,000, with many thousands more injured.
- 1998 U.S. embassy bombings: the bombings of the United States embassies in Dar es Salaam, Tanzania, and Nairobi, Kenya, kill 224 people and injure over 4,500; they are linked to terrorist Osama bin Laden, an exile of Saudi Arabia.
- August 15 – The Omagh bombing is carried out in Northern Ireland by the Real Irish Republican Army.
- December 4 – The Space Shuttle Endeavour launches the first American component to the International Space Station, the 25,600 pounds (11,600 kg) Unity module on STS-88. It docks with Zarya two days later.
- December 6 – Hugo Chávez, politician and former member of the Venezuelan military, is elected President of Venezuela.
- December 14 – The Yugoslav Army ambushes a column of 140 Kosovo Liberation Army militants attempting to smuggle arms from Albania into Kosovo, killing 36.
- December 16–19 – Iraq disarmament crisis: U.S. President Bill Clinton orders airstrikes on Iraq. UNSCOM withdraws all weapons inspectors from Iraq.
- December 19 – The U.S. House of Representatives forwards articles of impeachment against President Clinton to the Senate, making him the second president to be impeached in the nation.
- December 29 – Khmer Rouge leaders apologize for the post-Vietnam War genocide in Cambodia that killed more than one million people in the 1970s.
- December 31
- The first leap second since June 30, 1997, occurs.
- In the Eurozone, the currency rates of this day are fixed permanently.