999 (nine hundred [and] ninety-nine or nine-nine-nine) is a natural number following 998 and preceding 1000. The largest 3-digit decimal integer.

• , a Kaprekar number.^[1]
• A palindromic number in bases 10, 14 (515₁₄), and 36 (RR₃₆).
  • A repdigit in bases 10 and 36.
• The largest number in English not containing the letter 'o' in its name, when using short scale.
• A base-10 Harshad number because , a whole number.

• In some parts of the world, such as the UK and Commonwealth countries, 999 (pronounced as 9-9-9) is the main emergency telephone number, it also functions in many other countries.
• 999 was a London punk band active during the 1970s.
• 999 is also the short name for the visual novel Nine Hours, Nine Persons, Nine Doors.
• 999 is the last 3 digit number. It is also the last number in English written without a comma, as numbers above 999 must require a comma (e.g. numbers starting from 1,000 or more).
• 999 is the number the late rapper Juice WRLD chose as his moto, he explains it as "999 is 666 (the devil's number flipped upside down) to resemble taking a bad/unpleasant situation and turning it upside down turning it into a better situation."