GNU General Public License (GPL) Explained in Plain English (2026)

The GNU General Public License (GPL) is one of the most important software licenses ever written. It guarantees your freedom to use, share and change free software, and it powers projects like Linux and WordPress, which runs this site. When we first wrote about it in 2005, open source was still niche. Here’s what the GPL means in 2026, in plain English. (This is a general overview, not legal advice.)

Quick answer: The GPL is a free software license from the Free Software Foundation. Anyone may run, study, share and modify GPL software, even commercially. The catch is “copyleft”: if you distribute a modified version, you must release it under the GPL too and provide the source code. The two common versions are GPLv2 (used by Linux and WordPress) and GPLv3 (adds patent and anti-lockdown terms).

The four freedoms

1. Run the program for any purpose.
2. Study how it works and change it (requires access to the source code).
3. Redistribute copies.
4. Distribute your modified versions.

What copyleft means

Copyleft uses copyright law to keep software free. If you share a modified GPL program, the recipients get the same freedoms you had. You can’t take GPL code, change it and release it as closed source.

GPLv2 vs GPLv3

• GPLv2 (1991): used by the Linux kernel and WordPress (“GPLv2 or later”).
• GPLv3 (2007): adds explicit patent licences, compatibility with more licences and rules against “tivoisation” (hardware that blocks modified software).
• LGPL: a weaker variant that lets non-GPL programs link to a library.
• AGPL: extends copyleft to software used over a network, like web apps.

What you can and can’t do

• Can: use GPL software in your business, charge for distribution or support, modify it for private use without sharing.
• Must: include the licence and provide source code when you distribute binaries.
• Can’t: add restrictions that take away users’ freedoms.

Why WordPress themes and plugins are GPL

WordPress is GPLv2 or later, and the WordPress project considers themes and plugins that build on it to be GPL too. That’s why premium plugins still ship under the GPL; buyers pay for updates and support. See our list of open source applications for Windows for more GPL software.

Read the full text on the GNU website, along with the list of free software licences.

FAQ

Is GPL software free of charge?

Usually, but “free” means freedom. You may sell GPL software as long as buyers get the same freedoms.

Can I use GPL code in a commercial app?

Yes, but if you distribute the app, the combined work generally must be GPL too.

What’s the difference between GPL and MIT licences?

MIT is permissive: you can use the code in closed-source products. GPL requires derivative works to stay open.