Qt: Making the right licensing decision

As the Qt legal gal I receive numerous questions from companies looking to use Qt, wanting to know which license makes the most sense for them. Obviously licensing can be a complex topic and there are specialists out there who are dedicated to this topic.

To help our existing and potential customers I put together a presentation at Dev Days to give an indication of licensing options for Qt.  Given the response at both events, I thought there is need enough to continue communicating about this topic, and to discuss with our community the rights and obligations of each of the licenses we offer.

With the release of Qt 4.5 we introduced the Lesser General Public License (LGPL) as a licensing option. We now have three licenses under which we make Qt available:

-    Commercial license
-    Lesser General Public License (LGPL) v. 2.1:
-    General Public License (GPL) v.3.0

We have uploaded my Dev Days presentation slides to Slideshare (embedded below) – they should provide an overview of the impacts of each license choice and the factors to be considered when deciding. In addition I have prepared a brief summary here so you can see for yourself. We have focused on the commercial license and the LGPL as those are the two that tend to generate questions. We are of course always willing to do more posts on this subject if the community requests it.


Here is a breakdown of our two main license options:

Commercial License
This is a proprietary license developed by Nokia. This is the license that comes when customers purchase Qt.


  • It is designed to allow licensees to keep all code private, and also includes support and upgrades for a one-year period.
  • Because Nokia is the developer of the commercial license agreement, we are also able to modify the license as part of the commercial negotiation process or tailor it to particular customer usage scenarios.
  • You have to purchase license seats from us and we license Qt on “a per developer and per platform” basis.  Contact our Qt Sales Team (qt-sales@nokia.com) for pricing and product information.

The LGPL is a license agreement written (and copyrighted) by the Free Software Foundation. The LGPL is a “copyleft” open source software license but is less restrictive than the GNU GPL.


  • The LGPL version 2.1 license was created by the Free Software Foundation and is copyrighted by them.  This means that the terms cannot be changed or negotiated by us.
  • Users can develop proprietary applications that dynamically link to the Qt libraries without having to release their application source code.
  • All modifications that are considered “works based on the Library” must be licensed under the LGPL v. 2.1 and need to be shared with downstream recipients in source code format (i.e. contributed back). In the Qt context this means that modifications made to Qt itself must be licensed under the terms of the LGPL.
  • If you are shipping an executable, you must include any data and utility programs needed for reproducing the executable (i.e. must provide components needed to recompile with a new version of the library) unless such data and utility programs are normally distributed with the major components of the operating system on which the executable runs
  • Copyrights and notices need to be maintained

Because the LGPL is a complex legal document, we always suggest that you have your legal counsel review the license prior to beginning development work to ensure that the LGPL is appropriate for your development project. Please note that once you begin with the LGPL you cannot then convert to a commercial license due to a restriction in our commercial license agreement.

Handy reference chart:


LGPL v. 2.1

GPL v.3.0

License cost License fee charged No licensing fee No licensing fee
Must provide source code for changes to Qt No, modifications can be closed Source code must be provided Source code must be provided
Can create proprietary applications Yes – no source code must be disclosed Yes – if dynamically linking to the Qt library No, application is subject to the GPL and source must be available
Support Yes, with a valid maintenance agreement Not included, but available separately for purchase Not included, but available separately for purchase
Charges for device runtimes Yes No, distribution is royalty free No, distribution is royalty free


Have a look through the slides and post any comments or questions you might have below and we will do our best to answer them. If there is sufficient volume then we will post a few follow up blog posts on this topic.

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