| Acronym | Definition |
|---|
| API | Application Programming Interface |
| API | Academic Performance Index |
| API | Active Pharmaceutical Ingredient |
| API | Allocation de Parent Isolé (French: Single Parent Allowance) |
| API | Année Polaire Internationale (French: International Polar Year; research project) |
| API | Advanced Passenger Information |
| API | Air Pollution Index |
| API | Alphabet Phonétique International (French: International Phonetic Alphabet) |
| API | Administración Portuaria Integral (Mexico) |
| API | Associazione Piccole e medie Industrie |
| API | Architectural Publications Index |
| API | Antecedent Precipitation Index |
| API | Asosiasi Pertekstilan Indonesia (Indonesian Textile Association) |
| API | Aviation Preflight Indoctrination |
| API | Association of Physicians of India |
| API | Australian Pharmaceutical Industries Ltd. |
| API | Air Photo Interpretation |
| API | Association Psychanalytique Internationale (International Psychoanalytical Association) |
| API | Anonima Petroli Italiana SpA (Rome, Italy) |
| API | Active Pharma Ingredient |
| API | Age Participation Index (UK) |
| API | Anderson Packaging, Inc. (Rockford, IL) |
| API | A Pleasing Interface |
| API | Announcement of Public Interest |
| API | Alice Paul Institute (Mount Laurel, NJ, USA) |
| API | Asset Performance Inc. (Vancouver, BC, Canada) |
| API | Aerial Photographic Interpretation (American Society of Photogrammetry and Remote Sensing) |
| API | Air Position Indicator |
| API | Asylum Policy Instruction (UK) |
| API | Average Price Index (describes growth rate, related to inflation measurements) |
| API | Alt Preset Insane (MP3 encoder preset) |
| API | Ankle Pressure Index |
| API | Acquisition Program Integration |
| API | Applied Planning International Inc. |
| API | Agricultural Price Index |
| API | Associated Press of India |
| API | Automation & Process Industriel (French: Industrial Automation & Process) |
| API | Advanced Pharmaceutical Ingredients |
| API | Association des Parents Indépendants (French: Independent Association of Parents) |
| API | After Project Initiation |
| API | American Pirate Industries |
| API | Absolute Position Indication |
| API | Authenticity Probability Index |
| API | Aircrew Position Indicator (USAF) |
| API | Applications, Programs and Indentures |
| API | Axial Power Indicator |
| API | Application Programmers Initiative |
| API | Arithmetic Polynomial Interpolation |
| API | Arab Payments and Securities Settlement Initiative |
| API | Application Process Instruction |
| API | Automated Physical Inventory |
| API | Automation Proficiency Improvement (US Postal Service) |
| API | Accountable Property Inventory |
| API | Annual Plan for Instruction |
| API | Advertisers Product Index |
| API | Agfa and Picker International |
| API | Alert Process Improvement (Sprint) |
| API | AssassinPokémon Initiative (Anti-Pokemon Organization) |
| API | Assistent Project Ingenieur (Dutch: Assistant Project Engineer) |
| API | Association of Physicians in Industry |
| API | Atlantic Paratrans of NYC, Inc |
| API | Availability Priority Index |
| API | Automating Peripherals Incorporated |
| API | Automated Pellet Inspection |
| API | Aisne Plastique Industrie (French: Aisne Plastic Industry; Aisne, France) |
| API | Asociación Pueblos Indios (Spanish: Indian Peoples' Association; Costa Rica) |
| API | Aromatic Polyimide Insulation |
| API | Angus Productions Inc. |
| API | Assistant Principal for Instruction |
| API | Application Process Integration |
| API | Alliance for the Polyurethanes Industry |
| API | Atmospheric Pressure Ionization |
| API | American Pain Institute |
| API | Appleton Papers, Inc. (Appleton, WI) |
| API | Armor-Piercing Incendiary (ammunition) |
| API | Arab Planning Institute (Kuwait) |
| API | Animal Protection Institute |
| API | American Press Institute |
| API | Application Program Interface |
| API | Asset Priority Index |
| API | Asia Pacific Initiative (various organizations) |
| API | American Prepaid Legal Services Institute |
| API | Alaska Psychiatric Institute |
| API | Audio Products International (various locations) |
| API | Attachment Parenting International |
| API | Avian and Pandemic Influenza |
| API | Australian Property Institute (professional body) |
| API | Ascendant Partners, Inc. |
| API | Advanced Polygraph Institute (Australia) |
| API | American Products, Inc. (Florida) |
| API | Apple Learning Interchange |
| API | Associated Press International |
| API | Analytical Profile Index (microbiology) |
| API | Arab Peace Initiative |
| API | Australian Public Intellectual Network (non-profit publisher) |
| API | Athletes' Performance Institute (Tempe, AZ) |
| API | A Positive Image (various organizations) |
| API | Annual Premium Income |
| API | Associate in Personal Insurance (insurance) |
| API | Annual Physical Inventory |
| API | American Paper Institute |
| API | American Petroleum Institute |
| API | Aircraft Platform Interface |
| API | Alabama Polytechnic Institute |
| API | Association of Play Industries |
| API | Application Interface (Department of State) |
| API | Asian Pacific Islander (club) |
| API | Application Programmer Interface (less common) |
| API | Asian and Pacific Islander (US Census usage) |