30 (thirty) is the natural number following 29 and preceding 31.
In mathematics
350px|thumb|30 is a square pyramidal number.
30 is an even, composite, a pronic number, and a primorial.
The SI prefix for 10<sup>30</sup> is Quetta- (Q), and for 10<sup>−30</sup> (i.e., the reciprocal of 10<sup>30</sup>) quecto (q). These numbers are the largest and smallest number to receive an SI prefix to date.
In other fields
Thirty is:
- Used (as –30–) to indicate the end of a newspaper (or broadcast) story, a copy editor's typographical notation
- The number of days in the months April, June, September and November (and in unusual circumstances February—see February 30). Although the number of days in a month vary, 30 is used to estimate months elapsing.
- In years of marriage, the pearl wedding anniversary
History and literature
- Age 30 is when Jewish priests traditionally start their service (according to Numbers 4:3).
- One of the rallying cries of the 1960s student/youth protest movement was the slogan, "Don't trust anyone over thirty".
- In The Myth of Sisyphus the French existentialist Albert Camus comments that the age of thirty is a crucial period in the life of a man, for at that age he gains a new awareness of the meaning of time.