CCL is licensed under terms consistent with BSD 3-Clause licensing. Since CCL uses various third party packages, there are constraints regarding how CCL software can be distributed and used. In particular, because CCL links against the GPL-licensed FFTW and GSL libraries, we cannot provide binary images of CCL without also adopting a GPL-style license. Fortunately, installation of these two packages on most platforms is straight-forward. CCL also uses the CLASS library, which has its own copyright and usage constraints, and so CCL users will need to install the CLASS library themselves. Since installing CLASS can sometimes be problematic, we provide an installation script, class_install.py. Note that use of the public version of the CLASS library has a citation requirement. Finally, CCL uses code from the FFTLog package. We have obtained permission from the FFTLog author to include modified versions of his source code.