But the arrival of the first decade mark of the new century, there's a small debate about usage.
Two thousand ten or twenty-ten?
At the open-air Christmas market in New York City's Union Square, buyers and sellers tried out both, in response to a reporter's questions.
"Twenty-ten," says Kate Carlson without hesitation.
Becky Sandler says that's "too edgy." She says, "I'd never say twenty-ten."
Plenty haven't made up their minds yet. Shirley Ozery laughs that she's just "living one day at a time."