66th is the ordinal form of the number 66. 66th or Sixty-sixth may also refer to:
A fraction, , equal to one of 66 equal parts
Geography 66th meridian east, a line of longitude 66th meridian west, a line of longitude 66th parallel north, a circle of latitude 66th parallel south, a circle of latitude 66th Street
Military 66th Army (Soviet Union) 66th Division (disambiguation) 66th Regiment (disambiguation)
Other 66th century 66th century BC
See also 66 (disambiguation)