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
  • Legacy, video games based on the TV series
• 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

• Hydestyle
• Hydesville
• Hydesville, CA
• Hydesville, California
• Hydetown
• Hydetown, PA
• Hydetown, Pennsylvania
• Hyde United
• Hyde-White, Wilfrid
• Hydon Ball
• Hydon's Ball
• H.Y.D.R.A.
• H.Y.D.R.A
• Hydra
• Hydra 70
• Hydra (astronomy)
• Hydra (biology)
• Hydra-Centaurus Supercluster
• Hydra (chess)
• HYDRA (comics)
• Hydra (comics)
• Hydra (constellation)
• Hydra constellation
• Hydragas
• Hydra (genus)