OPN is a three-letter acronym that may stand for:
- Osteopontin, a glycoprotein secreted by osteoblasts
- Object Process Network, a simulation model meta-language
- Other Procurement, Navy, a funding appropriate category
- Optics & Photonics News, a magazine
- OpenPHPNuke, a content management system
- In Catholicism, OPN is ora pro nobis (pray for us).
- It also stands for Ordering Part Number on AMD CPUs
- In modern medicine of Japan, OPN stands for operation nurse (ăȘăç,) specializes in managing and delivering surgical tools to surgeon.
- Oneohtrix Point Never, a musician
- Olivary pretectal nucleus, a nuclei in the pretectal area, or pretectum
- In mathematics, odd perfect number