Adopting an open-source licence

By Steve Crouch.

Which open-source licence should you use?

Deciding to release software under an open-source licence is an important step in the lifecycle of any software project. Equally important is the selection of an appropriate licence: one that will correctly represent your rights as the software's owner, and the rights of third-party developers.

Why write this guide?

We wrote this guide to give an overview of a subject that we think is important to software sustainability.

Balancing rights

Many developers aim to distribute their software through a publicly available source-code repository, such as SourceForge, Google Code, whereas some will use their own locally hosted code repository. Such a move requires a balance of rights. You typically want to protect your claim to ownership of the software, but want to allow free access to the source code. This allows third-party developers to adapt the software to meet their needs, and - the goal of much open-source development - contribute their changes and improvements back to your project. When choosing a licence, it is vitally important to consider how you intend your source code to be used.

The choice of open-source licences can appear bewildering at first. However, the licences come in a smaller number of types - flavours, if you will - and looking at a licence in this way can make your choice easier.

• Copyleft licence (e.g. GNU GPL): if the code is modified and distributed, the modified code must be distributed under the same licence as the original code.
• Permissive licence (e.g. MIT): allows modifications and reuse on a broader scale.
• Partial or weak copyleft licence (e.g. Mozilla MPL): if the code is modified and distributed, any original files must be distributed under the original licence, but any new files introduced by third parties may be distributed under a different licence.

If you would like help determining which licence to use, we recommend contacting OSS Watch. OSS Watch are a public (and free) service for higher and further education institutions in the UK, which was created to help institutions and projects that use or develop free and open-source software. A number of helpful guides that describe important aspects of intellectual property and its application to software are available from OSS Watch. The following guides are particularly useful for helping with software licences:

• An overview of Intellectual Property Rights (IPR)
• Releasing you code under an open-source licence

OSS Watch also provide a list of web-based resources that describe more advanced aspects of licencing, such as dual licencing and contributor-licence agreements, and patents:

Resources on Intellectual Property Rights (IPR), licensing and patents