SISThe initials SIS may stand for:
- Swedish Standards Institute (earlier named Standardiseringskommissionen i Sverige).
- Schengen Information System.
- Secret Intelligence Service (MI6).
- Security Intelligence Service (espionage New Zealand style)
- Signals Intelligence Service. This United States Army group, led by William F. Friedman, broke the Japanese Foreign Office cypher called Purple. It eventually became a part of the NSA.