The licenses described in this chapter are very different from those described in Chapter 2. These licenses impose substantial limitations on those who create and distribute derivative works based on works that use these licenses. The GNU General Public License (the GPL License) explicitly requires that derivative works be distributed under the terms of the GPL License and also that derivative works may only be permitted to be distributed under the terms of the license. The Mozilla License imposes different and less restrictive terms on the licensing of derivative works. Both of these licenses (and a variation of the GPL License) are described in some detail in the following sections.

Before going into detailed descriptions of these licenses and their effects, it's a good idea to re-examine the limitations imposed by the licenses described in the previous chapter, if only for contrast.

The MIT License, probably the simplest of those licenses, imposes almost no restrictions on licensees and no meaningful restriction at all on licensees distributing derivative works. When the original work or "substantial portions" of it are distributed, the licensee is required to include a copyright notice and the notice giving permission to potential licensees of their rights to use the work. The licensee is not even required to include the disclaimer of warranties that was part of the original license. (Such licensees may, however, have good ...