GNU Lesser General Public License
lastmod 2025-05-19created 2014-05-038 edits
The GNU Lesser General Public License (formerly the GNU Library General Public License, LGPL) is a free software license of the Free Software Foundation.
The LGPL was created as a compromise between the strong copyleft terms of the GNU General Public License and the simple permissions of the BSD license or the MIT License. It was written in 1991 by Richard Stallman with legal advice from Eben Moglen, and revised again in 1999.
The LGPL places copyleft restrictions on the program itself, but does not apply copyleft to other programs that use it. However, there are still some restrictions on the latter programs.
The LGPL is used mainly for software libraries, and occasionally for standalone programs. Mozilla and OpenOffice are representative examples.
Preamble
When a program is linked with a library, whether statically or using a shared library, the combination of the two is legally speaking a combined work, a derivative of the original library. The ordinary General Public License therefore permits such linking only if the entire combination fits its criteria of freedom. The Lesser General Public License permits more lax criteria for linking other code with the library.
On the obligation to provide source code when using dynamic libraries
- Frequently Asked Questions about the GNU Licenses - GNU Project - Free Software Foundation
- Kakao Open Source Guide
The LGPL-2.1 license carries a notice obligation along with an obligation to disclose the full code (when used via dynamic linking, only the library in question must be disclosed).
Document
- Frequently Asked Questions about the GPL
- GNU Lesser General Public License
- Why you shouldn't use the LGPL for your next library
Question about using images under the LGPL license
Related answer: I called the Korea Copyright Commission, and they said licenses like the GPL or LGPL are not usually applied to images. They told me that for LGPL or GPL images, you just need to clearly state the source when using them.