The core language is. The libraries are another matter. From the website: The core of the Julia implementation is licensed under the MIT license. Various libr

The core language is. The libraries are another matter. From the website: The core of the Julia implementation is licensed under the MIT license. Various libraries used by the Julia environment include their own licenses such as the GPL, LGPL, and BSD (therefore the environment, which consists of the language, user interfaces, and libraries, is under the GPL).