What I found is that there are a variety of different licenses out there, and selecting one depends on the author's preference for the project. One of the goals of Chirp is to make the hardware, software, and firmware freely available for others to learn and grow the project.

A great resource for this was www.opensource.org, especially their FAQ page. In addition, this page was helpful in narrowing down the license that we wanted to use for Chirp.

Ultimately, we wanted to use Copyleft and decided on the GPLv3 because we wanted to make sure that derivative work is made available under the same terms.

Implementing the license was straight forward, we added a copyright and boilerplate heading to every source file and attached a copy of the GPLv3 license in a file named `COPYING`.