Seidō, Seido can mean:
- Seidō juku, a style of traditional karate founded by Tadashi Nakamura.
- Seidokaikan, a style of full contact karate founded by Kazuyoshi Ishii.
- Kyushu Seido-kai, a yakuza organization based in Kyushu
- A fictional high school from Battlefield Baseball
- A realm in the fictional universe of Mortal Kombat
SEIDO, Subprocuraduría Especializada en Investigación de Delincuencia Organizada (English: Assistant Attorney General's Office for Special Investigations on Organized Crime), is the organized-crime division of Mexico's Office of the Attorney General.
In October 2012, the organization changed its name from SIEDO to SEIDO.