NPI
- Gramm–Leach–Bliley Act
- NP-intermediate
- NPI-1
- Narcissistic Personality Inventory
- National Policy Institute
- National Provider Identifier
- National pollutant inventory
- Negative polarity item
- New Policy Institute
- New Politics Initiative
- New product introduction
- Nickel pig iron
- Non-pharmaceutical intervention
- Non-pharmaceutical intervention (epidemiology)
- Non-profit institution
- Nordic Patent Institute
- Northwest Progressive Institute
- Norwegian Polar Institute
- Nottingham Prognostic Index
- Numbering plan