GNU Guile is the preferred extension system for the GNU Project, which features an implementation of the Scheme programming language. In addition to large parts of Scheme standards, Guile Scheme includes modularized extensions for many different programming tasks. As GNU Guile became such a big project over the years, we had to split this reference manual in two parts that are two separate physical books. To keep it consistent with the digital manual, the references and page numbers cover both physical books as it were one. Therefore please note that you probably want to have both parts.