YY
JJ is an abbreviation for:
- Jiu Jitsu , a Japanese martial art
- Ju-Jutsu , a German martial art
- Jesu Juva , a Latin phrase
- Jeff Jarrett , an American professional wrestler
- JJ (band) , a Swedish band
- JJ (magazine) , a Japanese magazine
- JJ1 , a brown bear who immigrated to Germany in 2006
- Jason Jr. , the Woods Hole Oceanographic Institution's unmanned diving robot
- a manufacturer of cathode ray tubes, State Combine for Electromechanical Products in the Czechoslovak Republic, see Tesla as
- for the Texas Hold'em poker starting hand Bube Bube (English Jack Jack, also "Jay Jay")
- the Brazilian airline TAM Linhas Aéreas under the IATA airport code
- the German band Jupiter Jones
YY as a distinguishing mark on license plates:
- Norway: Gjøvik in the province of Innlandet