Open Source Development | Open Source License

What to Consider

The Qt framework is available under both open source and commercial licenses. This dual-licensing model is based on the principle of quid pro quo – roughly meaning “something for something.”

Simply put, this is how it works: In return for the value you receive from using Qt to create your application, you are expected to give back by contributing to Qt or buying Qt.

Contribution via Open Source

When selecting an open source license for your project, you contribute to free and open source software development by using Qt under any of the following licenses: LGPL version 3, GPL version 2 and GPL version 3.

Basic Premises of the Qt Open Source Model

GPL – All users have the rights to obtain, modify and redistribute the full source code of your application. Your users are granted rights founded on the four freedoms of the GNU General Public License.

LGPL – Any modification to a Qt component covered by the GNU Lesser General Public License must be contributed back to the community. This is the primary open source Qt license, which covers the majority of Qt modules.

Check out which components are available under the different open source models in the Qt Product Map.

Please note that there are parts of Qt that are only provided under GPL for open source users that will require you to license your application under a GPL compatible license. Qt also ships with third party open source components that might require respective licensing compliancy, if used. See details of other licenses inside Qt.

Open Source Usage Obligations

The majority of the Qt modules are available under the LGPL v3 and GPL v3 open source license. When developing under this license your obligations are to:

Provide a re-linking mechanism for Qt libraries
Provide a license copy & explicitly acknowledge Qt use
Make a Qt source code copy available for customers
Accept that Qt source code modifications are non-proprietary
Make “open” consumer devices
Accept Digital Rights Management terms, please see the GPL FAQ
Take special consideration when attempting to enforce software patents FAQ

If the open source license model isn't the right fit for your project or you have concerns about being able to comply to the license terms, contact us. We can help you secure rights to develop, use and distribute your application under a choice of commercial license packages.

Your Contributions Matter

Since our funding comes from selling commercial licenses and services, it is essential that we reach commercial readiness as quickly as possible. This can only be achieved through active community participation in our development process. The Qt community plays a vital role in ensuring the stability, richness and quality of Qt. With Qt releases being thoroughly tested by thousands of open source developers around the world, we get the boost needed to support the cost of driving further development of Qt. It ensures the future of Qt. We call this our Virtuous Cycle.

Visit the Contribution Wiki

Due Diligence

Confirm that you can abide by the obligations of Qt open source licensing. When deciding which license to use, please check your corporate open source policy or consult a software licensing legal expert.

Qt Licensing & Open Source Obligations

Source Code

Grab the code, or if you need help, the community not only contributes to Qt, but also to the Qt Wiki where you can learn how to get started.

Get the Source Code

Start Contributing

Qt source code repositories are open to the public, which means that you can immediately help guide and shape the future development of Qt by contributing code, translations, examples and more.

Learn More About Contributing

Frequently Asked Questions

Why is Qt licensed also under an open source license?

Qt Open Source Licensing
Popular

We believe in the Free Software movement where using software comes with certain rights, but also certain obligations. Use of open source licensing gives users four primary degrees of freedom when using Qt applications or devices:

The freedom to run the program for any purpose
The freedom to study how the program works and adapt it to specific needs
The freedom to redistribute copies so you can help your neighbor
The freedom to improve the program and release your improvements to the public, so that the whole community benefits

The freedoms are non-negotiable and absolute, the freedoms cannot be enjoyed selectively or partially, you also need to pass them to your users.

The Free Software community has thrived because of these rules, but there are also developers who never intend to observe or cannot comply to these rules, and thus should get a commercial license. The Qt Company exists to support both sets with the dual offering.

Why do you have an agreement with KDE about your licensing? What KDE is and what’s the history of Qt and KDE?

Qt Open Source Licensing

KDE (kde.org) is an international free software community, founded in 1996, producing an integrated set of cross-platform applications for desktop. KDE is mainly known for its Plasma Desktop environment, which is provided as the default work environment on many Linux distributions. KDE software is based on the Qt framework. In the early days of Qt, the KDE project and community were the biggest driving force in building the developer ecosystem around Qt.

In the very early days, Qt was already dual-licensed, but the source code was available under proprietary open source licenses. Compromises with KDE were sought to ensure that Qt would be available for their use under appropriate open source licensing even if Trolltech (the company that founded Qt) would be acquired or go bankrupt. As a result, the KDE Free Qt Foundation was founded and the KDE Free Qt Foundation Agreement created.

The KDE Free Qt Foundation is an organization with the purpose of securing the availability of the Qt toolkit for the development of Free Software and in particular for the development of KDE software. The Foundation was originally founded by Trolltech and the KDE e.V. (the legal non-profit organization behind KDE) in 1998 and it has a license agreement that ensures the availability of Qt under LGPLv3 and GPLv3 licenses for major desktop and mobile platforms. The license agreement has been updated couple of times over the years, mainly because of acquisitions around Qt or updates to licenses and platforms.

What is the consequence of not complying with the LGPL/GPL restrictions?

Qt Open Source Licensing

If software using these open source licensed libraries does not fully comply with the license obligations, you will lose your license and related distribution rights. It is also good to note that in most countries copyright infringement is statutory violation, not breach of contract and thus the statutory remedies apply.

You can find more information about GPL from GPL FAQ https://www.gnu.org/licenses/gpl-faq.html

What is the difference between LGPLv2 and LGPLv3?

Qt Open Source Licensing

LGPLv3 is the current version of the GNU Lesser General Public License. LGPLv2.1 is an older version and not recommended by the Free Software Foundation for new projects anymore. Both licenses have the same intention, namely to protect the freedom of users to use and modify the software licensed under LGPL.

LGPLv3 makes this intention very explicit. You have to provide means to the end user to install a modified version of the library licensed under LGPLv3 and run your software using that modified library. In practice, this for example refers to:

Tivoization – Explicitly not allowing creation of closed devices where the end user does not have the LGPL granted rights for the Qt open s