66 (sixty-six) is the natural number following 65 and preceding 67.

66 is a sphenic number,a semiperfect number,^[1] and a Erdős–Woods number.^[2]

• Messier object Spiral Galaxy M66, a magnitude 10.0 galaxy in the constellation Leo.
• The New General Catalogue object^[3] NGC 66, a peculiar barred spiral galaxy in the constellation Cetus.
• 66 Maja, a carbonaceous background asteroid from the central regions of the asteroid belt.

• The atomic number of dysprosium, a lanthanide.

66 (more specifically 66.667) megahertz (MHz) is a common divisor for the front side bus (FSB) speed, overall central processing unit (CPU) speed, and base bus speed. On a Core 2 CPU, and a Core 2 motherboard, the FSB is 1066 MHz (~16 × 66 MHz), the memory speed is usually 666.67 MHz (~10 × 66 MHz), and the processor speed ranges from 1.86 gigahertz (GHz) (~66 MHz × 28) to 2.93 GHz (~66 MHz × 44), in 266 MHz (~66 MHz × 4) increments.

• The designation of the historic U.S. Route 66, dubbed the "Mother Road" by novelist John Steinbeck, and other roads.
• Phillips 66, a brand of gasoline and service station in the United States.

• The total number of chapters in the Book of Isaiah in the Old Testament of the Bible.
• The number of verses in Chapter 3 of the Book of Lamentations in the Old Testament.
• The total number of books in the Protestant edition of the Bible (Old Testament and New Testament) combined.^{[citation needed]}
• In Abjad numerals, The Name Of Allah (الله) numeric value is 66.

• The number of the laps of the Spanish Grand Prix.
• The longest field goal made in NFL history was 66 yards and kicked by Justin Tucker.

• Sixty Six is a 2006 British movie about a bar mitzvah in London on the day of the 1966 World Cup final.
• In the Star Wars movie series, Order 66 is a prepared order to the clone troopers to kill the Jedi commanding them.

• AD 66
• 66 BC
• 1966
• 2066

• Route 66 was a popular US television series on CBS from 1960 to 1964.

• In the video game Fullmetal Alchemist, elusive villain Barry the Chopper is imprisoned in cell number 66, which later becomes his alias when battling the brothers at Laboratory Five.

• 66 (property) [zh], properties in China developed by Hang Lung Properties.
• The international direct dialing (IDD) code for Thailand.
• The number of the French department Pyrénées-Orientales.
• The name of a German card game, translated from sechsundsechzig (see Sixty-six (game)).
• In telecommunications a 66 block is used to organize telephone lines.
• Sergio Mendes and Brasil '66 was a 1960s group.
• 66 WNBC radio was a popular New York radio station, which became WFAN on 1 July 1987.
• Lil B has a song entitled "OMG 66".
• "Sixty-Six" is a song by Pat Metheny (born 1954) from his 2020 album From This Place.
• Le 66 is an opérette in one act of 1856 with music by Jacques Offenbach and a French libretto by Pittaud de Forges and Laurencin.
• In the horror genre and Western esotericism there are 66 legions of demons/spirits that Baal controls.^[4][5]

• Media related to 66 (number) at Wikimedia Commons