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
Media
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
Film and television 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
Music 999 (band), a London punk rock band active since the 1970s 999 (album), a self-titled album by the band 999 999 (EP), an EP by Olamide 999 (MC Lars album), an album by MC Lars 999 (Selena Gomez and Camilo song) "999" (Kent song) "999", a song from Keith Richards' album Main Offender (1992) 999, a number often used by Juice WRLD
Video games
999: Nine Hours, Nine Persons, Nine Doors, a 2009 video game developed by Chunsoft
Transportation 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
Other uses 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
See also 0.999... for proofs that 0.999... is equal to 1