The Processing development environment is released as open source under the GPL. The export libraries (also known as 'core') are released under an LGPL license, which means they can be used as a library and included in your project without you having to open up your code (though we encourage people to share anyway). But if you make changes to core, you have to submit back to us. More information about the GNU Public License can be found at www.gnu.org/copyleft/gpl.html.

The source code is stored on our developer site, and more information about its use can be found over there.

We need help! Having shared all the code and made it available for free, doesn't it just make you want to pitch in and help? We have too much work to do and can't keep up with things. We love to see bug fixes, new libraries, etc. If you're interested, contact us via the discourse section of the site.

The source code for the libraries is also included with the Processing software itself, should you want to modify them for your own use. If you want to modify the library for your own use, you can include the .java file as part of your sketch. Just be sure to remove the "package processing.xx;" line at the beginning. The Processing environment does not allow packages.