"The internal components are those created by Google
specifically for the Android project; the external components are
by and large other open source projects. Two major external
components -- the Linux kernel and WebKit -- are governed by
reciprocal licenses (GPLv2 and the Lesser General Public License).
In addition to the two major external components, an additional 30
or more internal components (including dbus, grub, emma, e2fsprogs,
bluez, Bison), also use reciprocal licenses. Twenty eight
components use the GPL and five use the LGPL, while others use
non-open-source licenses such as the OpenSSL and the Bzip2
"All of which means there is more complexity under the covers
than you might expect. Hence the management of hundreds of
components, multiple licenses, and associated obligations presents
challenges for developers and device manufacturers that use
Android, as well as the third-party companies that develop software
components for device manufacturers."