+@node Package Modules
+@section Package Modules
+
+From a programming viewpoint, the package definitions of the
+GNU distribution are provided by Guile modules in the @code{(gnu packages
+@dots{})} name space@footnote{Note that packages under the @code{(gnu
+packages @dots{})} module name space are not necessarily ``GNU
+packages''. This module naming scheme follows the usual Guile module
+naming convention: @code{gnu} means that these modules are distributed
+as part of the GNU system, and @code{packages} identifies modules that
+define packages.} (@pxref{Modules, Guile modules,, guile, GNU Guile
+Reference Manual}). For instance, the @code{(gnu packages emacs)}
+module exports a variable named @code{emacs}, which is bound to a
+@code{<package>} object (@pxref{Defining Packages}).
+
+The @code{(gnu packages @dots{})} module name space is
+automatically scanned for packages by the command-line tools. For
+instance, when running @code{guix package -i emacs}, all the @code{(gnu
+packages @dots{})} modules are scanned until one that exports a package
+object whose name is @code{emacs} is found. This package search
+facility is implemented in the @code{(gnu packages)} module.
+
+@cindex customization, of packages
+@cindex package module search path
+Users can store package definitions in modules with different
+names---e.g., @code{(my-packages emacs)}@footnote{Note that the file
+name and module name must match. For instance, the @code{(my-packages
+emacs)} module must be stored in a @file{my-packages/emacs.scm} file
+relative to the load path specified with @option{--load-path} or
+@code{GUIX_PACKAGE_PATH}. @xref{Modules and the File System,,,
+guile, GNU Guile Reference Manual}, for details.}. There are two ways to make
+these package definitions visible to the user interfaces:
+
+@enumerate
+@item
+By adding the directory containing your package modules to the search path
+with the @code{-L} flag of @command{guix package} and other commands
+(@pxref{Common Build Options}), or by setting the @code{GUIX_PACKAGE_PATH}
+environment variable described below.
+
+@item
+By defining a @dfn{channel} and configuring @command{guix pull} so that it
+pulls from it. A channel is essentially a Git repository containing package
+modules. @xref{Channels}, for more information on how to define and use
+channels.
+@end enumerate
+
+@code{GUIX_PACKAGE_PATH} works similarly to other search path variables:
+
+@defvr {Environment Variable} GUIX_PACKAGE_PATH
+This is a colon-separated list of directories to search for additional
+package modules. Directories listed in this variable take precedence
+over the own modules of the distribution.
+@end defvr
+
+The distribution is fully @dfn{bootstrapped} and @dfn{self-contained}:
+each package is built based solely on other packages in the
+distribution. The root of this dependency graph is a small set of
+@dfn{bootstrap binaries}, provided by the @code{(gnu packages
+bootstrap)} module. For more information on bootstrapping,
+@pxref{Bootstrapping}.
+