21st is the ordinal form of the number 21. Twenty-first or 21st may also refer to:
A fraction, , equal to one of 21 equal parts 21st of the month, a recurring calendar date 21st birthday, the age of majority in a several countries
Geography 21st meridian east, a line of longitude 21st meridian west, a line of longitude 21st parallel north, a circle of latitude 21st parallel south, a circle of latitude 21st Avenue 21st Street (disambiguation)
Military Twenty-First Air Force 21st Army (disambiguation) 21st Battalion (disambiguation) 21st Division (disambiguation) 21st Regiment (disambiguation) 21st Squadron (disambiguation)
Other Twenty-first Amendment (disambiguation) Twenty-first Amendment to the United States Constitution 21st century 21st century BC
See also 21 (disambiguation) 21st Century (disambiguation)