From the introduction: Permission to copy, modify and distribute this document is granted solely through the use of the Open Game License 1.0a. This document provides an interface to the basic rules and materials needed to create content compatible with the modern setting based on the best-selling tabletop RPG system in the world. This material is being released using the Open Gaming License Version 1.0a and you should read and understand the terms of that license before using this material. The text of the Open Gaming License itself is not Open Game Content. Instructions on using the License are provided within the License itself. All of the rest of the text in this document is Open Game Content as described in Section 1(d) of the License.