Psi
- CMX DVD
- Chebyshev function
- Dedekind psi function
- Digamma function
- Directive on the re-use of public sector information
- Indonesian Socialist Party
- Indonesian Solidarity Party
- Italian Socialist Party
- Italian Socialist Party (2007)
- J/psi meson
- Judge Dredd
- Kullback–Leibler divergence
- Office of Public Sector Information
- PS1 (disambiguation)
- PSI (album)
- PSI (computational chemistry)
- PSI (prion)
- PSI Records
- PSI Seminars
- PSI-20
- Pandemic severity index
- Paranormal Site Investigators
- Parasocial interaction
- Paul Scherrer Institute
- Pechersk School International
- Permanent staff instructor
- Personalized System of Instruction
- Photosystem I
- Physics Society of Iran
- Pitchshifter
- Planetary Science Institute
- Pneumonia severity index
- Poetry Slam, Inc.
- Policy Studies Institute
- Pollutant Standards Index
- Polygamma function
- Population Services International
- Porous silicon
- Potentially Shippable Increment
- Pound per square inch
- Pre-shipment inspection
- Present serviceability index
- Presentence investigation report
- Private sector involvement
- Private set intersection
- Professional Skills Institute
- Program-specific information
- Proliferation Security Initiative
- Protein Structure Initiative
- Proto-Siouan language
- Prudential Securities Incorporated
- Psi (Cyrillic)
- Psi (Greek)
- Psi (TV series)
- Psi (comics)
- Psi (instant messaging client)
- Psi (parapsychology)
- Psi Chi
- Psi Com
- Psi Corps
- Psi Islands
- Psi Lords
- Psi Power
- Psi Records
- Psi hit
- Psi-Force
- Psi-Hawk
- Psi-theory
- Psy (disambiguation)
- Psychiatric Solutions, Inc.
- Psychology
- Public Services International
- Reciprocal Fibonacci constant
- Scaled and Icy
- Statisticians in the Pharmaceutical Industry
- Stream function
- Supergolden ratio
- Tait-Bryan angles
- Tangential angle
- United States Senate Homeland Security Permanent Subcommittee on Investigations
- Water potential
- Wave function