YJ or yJ may refer to:
Arts and entertainment:
- Yahoo! Japan, a website
- Young Justice, a DC comic series
- Young Justice (TV series), TV series aired on Cartoon Network
- Young Justice: Legacy, video games based on the TV series
- Young Justice (TV series), TV series aired on Cartoon Network
- Yakitate!! Japan, an anime
- Weekly Young Jump, a magazine
Other uses:
- Yoctojoule (yJ = 10−24 J), an SI unit of energy
- Yottajoule (YJ = 1024 J), an SI unit of energy
- Jeep Wrangler, an SUV
- Young Judaea, a Zionist youth movement