999

999 or triple nine most often refers to:

999 (emergency telephone number), a telephone number for the emergency services in several countries
999 (number), an integer
AD 999, a year
999 BC, a year

Books

999 (anthology) or 999: Twenty-nine Original Tales of Horror and Suspense, a 1999 anthology of short stories
Galaxy Express 999, a manga and anime created by Leiji Matsumoto

Triple 9, a 2016 heist-thriller film
999 (British TV series), a British programme presented by Michael Buerk that aired on the BBC
999 (Malaysian TV series), a 2004 Malaysian crime reality television series
999: What's Your Emergency?, a 2012 British factual programme following the emergency service
Triple Nine (TV series), a Singaporean television series running from 1995 to 1999

Ducati 999, an Italian motorcycle
New York Central and Hudson River Railroad No. 999, the first steam locomotive in the United States to operate at faster than 100 mph
Ford 999, a pioneering 1902 racer named for the locomotive

999 Zachia, an asteroid
9–9–9 Plan, a tax plan proposed by 2012 Republican presidential candidate Herman Cain
999 phone charging myth, an urban myth that calling the emergency services charges mobile phones
Nine (purity), an informal way of ranking purity; "three nines" would be 99.9% pure
"Three nines" as a level of high availability (99.9%)
Triple Nine Society, a society for people with IQs in the 99.9th percentile
Nine Hours, Nine Persons, Nine Doors, a 2009 video game developed by Chunsoft