Valid copyright notices

Free software licenses rely on copyright law. The pro is that they are enforceable. The con is that you get the administrative burden. Fortunately, this merely means having in all your files:

  • a copyright notice: Copyright _year1_, _year2_, _year3_ _copyright-holder_
  • a license notice

About the year list: the FSF recommends listing every relevant year individually, but it is acceptable to use ranges (assuming every year in the range, inclusive, is covered, of course).

About the copyright-holder: the FSF recommends listing individual (real-world) names, or other entities with legal status, but it is acceptable to use ersatz identifiers like "Project Foo contributors" even when Project Foo has no legal existence. Using such fake identifiers makes the copyright less defendable in court. (Reference: https://lists.gnu.org/archive/html/savannah-hackers-public/2010-04/msg00005.html and related messages.)

Richard Stallman's Legal Matters section in the GNU maintainers guide is worth reading (although some parts are specific to GNU projects): http://www.gnu.org/prep/maintain/html_node/Legal-Matters.html

GNU GPL

In order to release your project properly and unambiguously under the GNU GPL, please place copyright notices and permission-to-copy statements at the beginning of every copyrightable file, usually any file more than 10 lines long.

In addition, if you haven't already, please include a copy of the plain text version of the GPL, available from http://www.gnu.org/licenses/gpl.txt, into a file named "COPYING".

For more information, see http://www.gnu.org/licenses/gpl-howto.html.

The GPL FAQ explains why these procedures must be followed. To learn why a copy of the GPL must be included with every copy of the code, for example, see http://www.gnu.org/licenses/gpl-faq.html#WhyMustIInclude.

GNU LGPL

In order to release your project properly and unambiguously under the LGPL, please place copyright notices and permission-to-copy statements at the beginning of every copyrightable file, usually any file more than 10 lines long.

In addition, if you haven't already, please include a copy of the plain text version of the GNU LGPL, available from http://www.gnu.org/licenses/lgpl.txt, into a file named "COPYING".

For more information, see http://www.gnu.org/licenses/lgpl.html#SEC4.

GFDL

In order to release your project properly and unambiguously under the GFDL, please place copyright notices and permission-to-copy statements after the title page of each work.

In addition, if you haven't already, please add a copy of the FDL (available from http://www.gnu.org/licenses/fdl.html in various formats) as a section of your works.

For more information, see http://www.gnu.org/licenses/fdl.html#SEC4

http://www.gnu.org/licenses/fdl-howto.html also covers additional points, including a smaller notice that you can use in auxiliary files.

Other licenses

If the license is small (such as the mBSD/MIT/Expat license), instead of a license notice, include it entirely at the top of all your files.

Binary files

If some of your files cannot carry such notices (e.g. binary files), then you can add a README file in the same directory containing the copyright and license notices. Check http://www.gnu.org/prep/maintain/html_node/Copyright-Notices.html for further information.