Das KDevelop-Programmierhandbuch: Leitfaden zur C++-Anwendungsentwicklung für das K Desktop Environment (KDE) mit Hilfe der KDevelop-IDE in der Version 1.2
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# 16.2. KDE and Qt Licensing Issues

Especially the Qt licensing caused a lot of trouble for the KDE development community until Qt 2.0 which comes with the new QPL license. The Troll Tech company, as the owner and creator of Qt, delivers the Unix version of the library free of charge, but with the restriction that you cannot change the delivered code and redistribute it without an explicit agreement on their side. This was the reason why many free software developers tended to condemn this licensing, as it wasn't absolutely free, especially to do any changes. On the other hand, the Qt library offers a lot of advantages that make it also very attractive for developing commercial applications:

- By buying a commercial license, you can write portable applications for Unix and Windows platforms

- The provided classes and application framework are providing a good solution for easy application design

- You can develop for Unices without being dependend on the GPL licensing when holding a commercial license

The KDE project on the other hand chose the Qt library as a base for developing a desktop environment for Unix systems as well as an extended application framework enhancing the facilities of the capabilities Qt provides. Developers can make use of KDE's advantages by using the provided libraries, distributed as the KDE libraries.

The KDE libraries themselves are distributed under the LGPL, the GNU Library General Public License. What does this mean to application developers ?

## 16.2.1. Non-commercial Development

For non-commercial development, the Qt library is provided free of charge. Your application can make use of the library as far as it does not change the library and the developer delivers his application sourcecode free of charge as well.

The LGPL of the KDE libraries ensures using the KDE libraries as well for non-commercial development. You can make use of the KDE libraries as you like to or your application may require.

## 16.2.2. Commercial Development

For commercial developement, the Troll Tech company offers buying a commercial license. This allows using the Qt library for development purposes as your application or project may require. You can ship your application in any form, as binaries only or by sourcecode, independed of any GPL licensing.

When using the KDE libraries, you have to watch the LGPL license, which explicitely allows commercial development using the library distributed under the LGPL. You just have to watch the rules of the license to know the restrictions that may arise when using the KDE libraries as a base for commercial application development based on KDE.

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