<p>The GNU General Public License (GPL) is the principal copyleft

license. Copyleft is a framework that permits ongoing sharing of a

published work, with clear permissions that <em>both</em> grant

<em>and</em> defend its users' freedoms &mdash; in contrast to other

free licenses that grant freedom but don't defend it.

Free software released under the GPL is fundamental

to modern technology, powering everything from laptops and desktops to

household appliances, cars, and mobile phones, to the foundations of

the Internet. Following the GPL's terms is easy — it gets more

complicated only when products distributed with GPL'd software also

include software distributed under terms that restrict users. Even in

these situations, many companies comply properly, but some companies

also try to bend or even break the GPL's rules to their perceived

advantage.</p>

<p>The Free Software Foundation (FSF) and Software Freedom Conservancy

  (Conservancy) today lead worldwide efforts to ensure compliance with

  the GPL family of licenses. The FSF began copyleft enforcement

  in the 1980s, and Conservancy has enforced the GPL for many of

  its member projects since its founding nearly a decade ago. Last

  year, the FSF and Conservancy jointly

  published <a href="https://copyleft.org/guide/"><cite>Copyleft and

  the GNU General Public License: A Comprehensive Tutorial and

  &ldquo;<a href="https://copyleft.org/guide/comprehensive-gpl-guidepa2.html#x17-116000II">A

  Practical Guide to GPL Compliance&rdquo;</a> and

  &ldquo;<a href="https://copyleft.org/guide/comprehensive-gpl-guidepa3.html#x26-152000III">Case

  Studies in GPL Enforcement</a>&rdquo;, which explain the typical

  process that both the FSF and Conservancy follow in their GPL

  enforcement actions. (Shorter descriptions of these processes appear

  in blog posts written

  by <a href="https://www.fsf.org/blogs/licensing/compliance-situations">the

  FSF</a>

  and <a href="https://sfconservancy.org/blog/2012/feb/01/gpl-enforcement/">Conservancy</a>.)</p>

<p>As stalwarts of the community's freedom, we act as a proxy for users when

companies impede the rights to copy, share, modify, and/or

redistribute copylefted software. We require all redistributors to

follow the GPL's requirements in order to protect all the users' freedom,

and secondarily to support businesses that respect freedom

while discouraging and penalizing bad actors.</p>

<p>Copyleft is based on copyright; it uses the power of copyright to

defend users' freedom to modify and redistribute rather than to hinder

modification and redistribution. A traditional copyright license is

violated by giving the work to others without permission; a copyleft

license is violated by imposing restrictions to <em>prevent</em>

further redistribution by others. Nevertheless, with their basis in copyright law,