This post begins a series on open source software licenses. Look forward to forthcoming posts covering more open source software licenses, as well as the differences between them.

First of all, what is an open source software license? Open source software licenses are a license that copyright holders (the original creators) apply to their software which generally allows users to make use of, change, and share the software with others without (much) limitation, while also making the source code available, but still protecting themselves from legal liability.

One of the most popular of such licenses is GNU’s General Public License. To see the complete language, visit Not only does this license make your software open source, but it also takes measures to ensure that it stays that way, even if someone modifies and redistributes it. This practice is known as “copyleft,” which grants licensees the right to freely use, change, and share the software, but it also requires licensees to provide the program, or any modified version, under the same license, in order to keep it freely distributable.

Now we will do an overview of the features and requirements of the latest version (v3) of the GNU GPL.

  • You must provide a full copy of the license with the program.
  • You must make the source code available to the user of the program.
  • You have the option to charge a fee for the program.
  • There is no warranty of any kind with the program, but one can be provided separately for a fee.
  • Any modified versions of the program must be clearly marked as such and licensed under the GNU GPL also.
  • Users can sell modified versions of the program or programs of their own containing code licensed under GNU GPL, if they provide the source code and users can freely redistribute and modify it just as under the GNU GPL.
  • Patents cannot be used to render the program non-freely usable, modifiable, or distributable.
  • Users have unlimited permission to run the software but if a user fails to comply with the license in some way, it is terminated. (Generally, if the user ceases all violations, the license is provisionally reinstated unless the copyright holder terminates your license completely within 60 days.)
  • All recipients of the program are automatically granted this license to use the program.
  • There is a limited ability to supplement the license with additional terms.
  • The option to use either the stated version of the license or any future versions of the GNU GPL is provided within the license.
  • Your liability is limited by this license.

In order to use the GNU GPL for your software you must include all of the following language in your program and at least the first section below in each file, along with a notation to where the complete notice and license can be located. You should also provide information on how you can be contacted as well.

<one line to give the program’s name and a brief idea of what it does.> Copyright (C) <year>  <name of author>

    This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program.  If not, see <>. 

If you have any questions about deciding on a license or creating specialized license for your software, contact the Law Office of E.C. Lewis, PC, home of your Denver Small Business Lawyer, Elizabeth Lewis at 720-258-6647 or email her at