The earliest roots of OpenPGP trace back to *"Pretty Good Privacy (PGP)"*, a software program written by [Phil Zimmermann](https://en.wikipedia.org/wiki/Phil_Zimmermann) and first released in 1991.
The original PGP software has played a role in the political struggles sometimes referred to as the ["Crypto Wars"](https://en.wikipedia.org/wiki/Crypto_Wars) (also see https://en.wikipedia.org/wiki/Crypto_(book) for some of that history, including about the history of PGP).
The ownership and branding of the product has [changed over the years](https://en.wikipedia.org/wiki/Pretty_Good_Privacy#PGP_Corporation_and_Symantec). The software enjoys a continued existence, albeit with [changing name and scope](https://en.wikipedia.org/wiki/Pretty_Good_Privacy#PGP_Corporation_encryption_applications).
While the original PGP software was developed as a commercial product, the owner at the time, "PGP Inc." started a standardization effort with the IETF in July 1997.
The resulting open standard was named [OpenPGP](https://en.wikipedia.org/wiki/Pretty_Good_Privacy#OpenPGP).
The result of this early standardization work is [RFC 2440 "OpenPGP Message Format"](https://datatracker.ietf.org/doc/html/rfc2440), published November 1998. RFC 2440 describes OpenPGP version 3.
GnuPG has been the major Free Software implementation of OpenPGP for a period of time. It has played an important (and successful) role in the release of NSA documents by [Edward Snowden](https://theintercept.com/2014/10/28/smuggling-snowden-secrets/).
Note: The terms "pgp key" and "gpg key" are often used interchangably. Since both PGP and GnuPG are just some out of many existing OpenPGP implementations, the proper term to use is "OpenPGP key".
- Protonmail, who provide email encryption services for a large number of users, use (and maintain) [OpenPGP.js](https://openpgpjs.org/)as well as [GopenPGP](https://gopenpgp.org/).
- The Thunderbird email software is using the [RNP](https://www.rnpgp.org/) implementation for their built-in OpenPGP support since version 78 (released in mid-2020).
- The RPM Package Manager software includes an OpenPGP backend based on [Sequoia PGP](https://sequoia-pgp.org/), a modern OpenPGP implementation in Rust. Fedora [uses Sequoia PGP in rpm](https://sequoia-pgp.org/blog/2023/04/27/rpm-sequoia/) since version 38.
As of this writing (in 2023), version 4 of OpenPGP is still most commonly used. OpenPGP version 4 is described in [RFC 4880](https://datatracker.ietf.org/doc/html/rfc4880).
All uses of OpenPGP are centered around (asymmetric) cryptographic key material. In OpenPGP, cryptographic keys are combined with additional metadata into "OpenPGP Keys", or "OpenPGP Certificates".
