Eleven European nations locked their currencies together and launched the euro as an electronic accounting currency, the boldest monetary experiment in modern history.

Poland, Hungary, and the Czech Republic formally joined NATO, the first former Warsaw Pact states to enter the Western alliance.

Two British students launched Neopets, a browser-based virtual pet site that became one of the earliest global social gaming phenomenons.

Czech Republic, Hungary, and Poland formally joined NATO, becoming the first former Warsaw Pact nations admitted into the Western military alliance.

Two students killed 12 classmates and a teacher and wounded 21 others at Columbine High School in Colorado before taking their own lives.

Distributed-computing project SETI@home, harnessing idle time on millions of home PCs, pushed forward its unprecedented volunteer search of Arecibo radio telescope data for signs of extraterrestrial signals.

Student protests erupted in Tehran after a hardline crackdown on a reformist newspaper, sparking the largest unrest since the 1979 revolution.

NASA's Chandra X-ray Observatory, launched days earlier aboard shuttle Columbia, reached its final elongated orbit, becoming the most powerful X-ray telescope ever built.

Portugal handed sovereignty over Macau to China after 442 years of colonial rule, ending the last European colonial presence in Asia.