I would like to create a plugin using commercial software.
Does the QGis licence permit this?
Are there any restrictions on the licence I can choose to apply to my plugin?
Foreword : I think you mean «proprietary» and not «commercial». Any opensource product can be a commercial product, even GPL ones.
You can write plugins for QGIS in C++ or Python, the latter being advised, as it simplifies plugins distribution and deployment.
QGIS is licenced as GPL, and the Python bindings are GPL too. So is PyQT, which is used in QGIS Python modules.
Therefore, any plugin written for QGIS, linking to QGIS C++ library, or importing QGIS python modules or PyQT modules has to be GPL too.
If you want to create a plugin using proprietary software, you can only do it if the link between your plugin and the proprietary software is loose.
You cannot :
You can :
The FSF faq answers a lot of questions regarding the GPL and what you can do with it (or not) :
As for Python, the Plone project ( http://www.plone.org ) has made some licence research and states in its licence FAQ that importing a GPL python module leads you to have to licence your code as GPL :
Note that having your code licenced under the GPL does NOT mean you must distribute it. But if you do, you have to provide the source code as GPL.