| Acronym | Definition |
|---|
| PSI | Pounds per Square Inch |
| PSI | Packet Switching Interface |
| PSI | Population Services International |
| PSI | Psychiatric Solutions Inc. |
| PSI | Public Services International |
| PSI | Product Stewardship Institute |
| PSI | Patient Safety Indicators |
| PSI | Public Sector Information |
| PSI | Policy Studies Institute (UK) |
| PSI | Paul Scherrer Institute (Switzerland, Joint Institute of ETH) |
| PSI | Pet Sitters International |
| PSI | Psionic |
| PSI | Pre-Shipment Inspection |
| PSI | Proliferation Security Initiative (international treaty with US DoD mission) |
| PSi | Performance Studies International |
| PSI | Performance Systems International |
| PSI | Penn State Industries |
| PSI | Presentence Investigation |
| PSI | Partito Socialista Italiano |
| PSI | Postpartum Support International |
| PSI | Pre-Sentence Investigation |
| PSI | Patient Safety Institute |
| PSI | Program Specific Information (Television) |
| PSI | Permanent Subcommittee on Investigations (US Senate) |
| PSI | Pneumonia Severity Index |
| PSI | Perspectives of System Informatics |
| PSI | Pitchshifter (band) |
| PSI | Programa Nacional para la Sociedad de la Información |
| PSI | Policy Studies Inc (Denver, Colorado) |
| PSI | Protein Structure Initiative |
| PSI | Personalized System of Instruction |
| PSI | Planetary Science Institute |
| PSI | Physical Sciences Inc. |
| PSI | Pollutant Standards Index |
| PSI | Psychological Society of Ireland |
| PSI | Paix et Securite Internationales (French) |
| PSI | Pharmaceutical Society of Ireland |
| PSI | Postponing Sexual Involvement |
| PSI | Process Safety Information |
| PSI | Planned Systems International (Columbia, MD) |
| PSI | Product Support Integrator (US Army) |
| PSI | Proteomics Standards Initiative |
| PSI | Phase Shifting Interferometry |
| PSI | Police Sub Inspector |
| PSI | Personnel Security Investigation |
| PSI | Pharmaceutical Security Institute |
| PSI | Promoting Social Inclusion (UK) |
| PSI | Professional Secretaries International |
| PSI | Private Sector Initiatives (Houston, TX) |
| PSI | Plant Sciences Institute |
| PSI | Public Safety Institute |
| PSI | Present Serviceability Index (pavement quality rating) |
| PSI | Professional Services Industries, Inc. |
| PSI | Statisticians in the Pharmaceutical Industry |
| PSI | Public Service Indiana |
| PSI | Pollution Standards Index |
| PSI | Planning Systems Incorporated |
| PSI | Patient Safety Initiatives |
| PSI | Pollution Standard Index |
| PSI | Polymer Search on the Internet |
| PSI | Patient Services Incorporated |
| PSI | Produkte Und Systeme Der Informationstechnologie (German stock company) |
| PSI | Physicians Services Incorporated (Canada) |
| PSI | Programmable Serial Interface |
| PSI | Portuguese Stock Index |
| PSI | Performance Sales International |
| PSI | Paul-Scherer-Institut (Switzerland) |
| PSI | Printempa Semajno Internacia |
| PSI | Public Service Interpreting |
| PSI | Aktiengesellschaft für Produkte und Systeme der Informationstechnologie |
| PSI | Project for School Innovation |
| PSI | Perception, Systèmes, Information |
| PSI | Philanthropic Service for Institutions |
| PSI | Protein Synthesis Inhibition |
| PSI | Pharmacy Services Inc. |
| PSI | Peripheral Solutions Inc. (Ontario, Canada) |
| PSI | Pakistan Standards Institution |
| PSI | Professional Scuba Inspectors, Inc. |
| PSI | Public Seed Initiative (USDA) |
| PSI | Professors for a Strong Israel |
| PSI | Psychiatric Society for Informatics |
| PSI | Photon Systems Instruments |
| PSI | Pipeline Systems Inc. |
| PSI | Political and Social Inquiry |
| PSI | Perfectly Scientific Inc. |
| PSI | Palestine Standards Institution |
| PSI | Philanthropic Studies Index |
| PSI | Plasma Source Instrument (NASA) |
| PSI | Para Su Información (Spanish: For Your Information) |
| PSI | Propagation Systems Inc. |
| PSI | Portable Scheme Interpreter |
| PSI | Project Status Inquiry |
| PSI | Portable Site Information |
| PSI | Program Structure Interface (integrated development environments) |
| PSI | Production/Sales/Inventory |
| PSI | Pitch Synchronous Innovation |
| PSI | Pechersk School International |
| PSI | Process Safety Incident |
| PSI | Pipeline Seal and Insulator, Inc. |
| PSI | Professional Support Inc. |
| PSI | Probabilistic and Statistical Inference |
| PSI | Professional Standards Institute |
| PSI | Permanent Staff Instructor (UK military) |
| PSI | Paranormal Science Investigations |
| PSI | Preliminary Site Inspection |
| PSI | Poseidon Scientific Instruments Pty Ltd |
| PSI | Process Safety Institute |
| PSI | Partit Socialista de les Illes (Catalan: Socialist Party of the Islands) |
| PSI | Parent Success Initiative |
| PSI | Product Support Initiative |
| PSI | Progressive Structural Inspection (airframe hour based maintenance and overhaul inspection) |
| PSI | Present Situations Index |
| PSI | Projeto de Sistemas de Informação |
| PSI | Pan-Sahelian Initiative |
| PSI | Professional Success Institute |
| PSI | Pre-Screening Interview |
| PSI | Premium Services Infrastructure |
| PSI | Program Security Instruction |
| PSI | Prism Solutions, Inc. |
| PSI | Personal Space Invader |
| PSI | Professional Staff Internship |
| PSI | Personnel Strategies LLC |
| PSI | Paradigm Shift International |
| PSI | Purchase, Sales and Inventory |
| PSI | Program in the Study of Imagination |
| PSI | Partisan Self Identification |
| PSI | Photon Simulation Interface |
| PSI | Process & Systems Integrity |
| PSI | Planar Spiral Inductor |
| PSI | Programmable Stratabus Interface |
| PSI | Prestige Software International |
| PSI | Public Studies Institute |
| PSI | Physical Site Identifier (used to identify a Navy or Marine Corps military installation) |
| PSI | Probability, Statistics and Information |
| PSI | Paranormal Society of Indiana |
| PSI | Pan-Saharan Initiative |
| PSI | Peripheral System Interconnect |
| PSI | Primary Shell Integrity |
| PSI | Philosophy Student Initiative |
| PSI | Pollution Standard Indicator |
| PSI | Process Sciences, Incorporated |
| PSI | PBX Switch Interface |
| PSI | Plan Speed Indicator |
| PSI | Programmed School Input |
| PSI | Promotional Services International |
| PSI | Pro Safety International Ltd (UK) |
| PSI | Pilot's Steering Indicator |
| PSI | Press Services of India (India) |
| PSI | PI Scientific Instrument |
| PSI | Property Standards Index (Australia) |
| PSI | President's Security Initiative |
| PSI | Pico-Second Interval |
| PSI | Program Support Item/Interest |
| PSI | Prior Suspense Item |
| PSI | Product-Specific Sales Incentive |
| PSI | ProScuba Inc. |
| PSI | Personal and Family Safety Information |
| PSI | Pro Salute Imperii (Latin: For Safety of the Empire, epigraphy) |
| PSI | Pleural Space Infection |
| PSI | Parallelization/Standardization/Integration |
| PSI | Programme de Surveillance de l'Irradiation (French: Radiation Monitoring Program) |
| PSI | Programme de Suivi de l'Irradiation (French: Irradiation Monitoring Program) |
| PSI | Political, Social and International Studies (various locations) |
| PSI | Potentially Shippable Increment (Agile Software Development) |
| PSI | Platform Solutions, Inc. (Massachusetts) |
| PSI | Public Strategies, Inc. (various locations) |
| PSI | Personal Software Inspector |
| PSI | Pharmaceutical Strategic Initiatives (est. 1985) |
| PSI | Plant Science Initiative |
| PSI | Personal Services Income (taxes) |
| PSI | Principal Security Inspector (aviation) |
| PSI | Photonic Systems, Inc. (Billerica, MA) |
| PSI | Pacific Sustainability Index (Claremont McKenna College; Claremont, CA) |
| PSI | Printing Services, Inc. (various locations) |
| PSI | Plastic Surgery Institute (various locations) |