XX or xx may refer to:
- 20 (number), Roman numeral XX
Film and TV
- XX (film), a 2017 anthology horror film
- "XX", an episode of CSI: Crime Scene Investigation (season 4)
- XX, the production code for the 1969 Doctor Who serial The Seeds of Death
- XX (web series), a 2020 South Korean web series
- XX (organization), a fictional organisation in the comic and game XIII
Genetics
- XX sex chromosomes, in the XY sex-determination system
- XX sex chromosomes, in the XO sex-determination system
- a female, an organism producing ova gametes that fuse with the male gamete during sexual reproduction, typically having two X chromosomes
- XX male syndrome, also known as de la Chapelle syndrome, a rare congenital intersex condition resulting in a phenotypical male with two X chromosomes
- XX gonadal dysgenesis, a type of female hypogonadism resulting in non-functioning ovaries
Music
- The xx, a British indie band
- X_______X (band), a Cleveland no wave band
Albums
- Toto XX, a 1998 album by Toto
- XX (Mushroomhead album), 2001
- xx (The xx album), 2009
- XX (Great Big Sea album), 2012
- XX – Two Decades of Love Metal, a 2012 compilation album by HIM
- XX (O.A.R. album), 2016
- XX (Mino album), 2018
- XX, a 2018 album by Note-oriety
- + + (EP), a 2018 EP, repackaged as [X X] in 2019, by Loona
Songs
- "xx", a song by Hayley Kiyoko from Expectations
- "XX", a song by Feid from Ferxxo (Vol 1: M.O.R)
Organisations
- XX Bomber Command, an inactive United States Air Force unit
- XX Corps (disambiguation)
- Legio XX Valeria Victrix or Legion XX, a legion of the Roman Empire
Other uses
- XX (novel), a 2020 novel by Rian Hughes
- XX System or Double-Cross System, a British deception operation in the Second World War
- Les XX, a group of twenty Belgian painters
- Dos Equis or XX, a brand of Mexican beer
xx, to express exponentiation in the initial version of the FORTRAN programming language