Copyleft是一由自由软件运动所发展的概念，是一种利用现有着作权体制来挑战该体制的授权方式，在自由软件授权方式中增加copyleft条款之后，该自由软件除了允许用户自由使用、散布、改作之外，copyleft条款更要求用户改作后的衍生作品必须要以同等的授权方式发布以回馈社区。

Copyleft的中文译法包括着佐权、反版权、版权属左、脱离版权、版权所无、版权左派、公共版权、著作留、著作续、版责、版可等。Copyleft授权方式虽然与常见的著作权授权模式不同：选择Copyleft授权方式并不代表作者放弃著作权，反而是贯彻始终，强制被授权者使用同样授权发布衍生作品，copyleft授权条款不反对著作权的基本体制，却是透过利用著作权法来进一步地促进创作自由。

Copyleft (a play on the word copyright) is the practice of offering people the right to freely distribute copies and modified versions of a work with the stipulation that the same rights be preserved in derivative works down the line.

Copyleft is a form of licensing, and can be used to maintain copyright conditions for works ranging from computer software, to documents, to art. In general, copyright law is used by an author to prohibit recipients from reproducing, adapting, or distributing copies of their work. In contrast, under copyleft, an author may give every person who receives a copy of the work permission to reproduce, adapt, or distribute it, with the accompanying requirement that any resulting copies or adaptations are also bound by the same licensing agreement.