"Copyleft" is a process invented by Free Software pioneer Richard Stallman, founder of the GNU Project at the Free Software Foundation, for the purpose of liberating information from the proprietary legal encumbrances associated with conventional copyright. Stallman's original intent was to create a body of software that may be freely shared among programmers, users, friends, and associates without violating the restrictive licensing agreements that typically limit the ways in which proprietary software may be used.

One of the consequences of Stallman's initiative has been the development of the highly robust and commercially successful Free Software movement, and the in some ways parallel Open Source movement. (See Stallman's article, "Why 'Free Software' is better than 'Open Source'" for commentary on the differences and similarities between Free Software and Open Source Software.) The Freedom of Free Software may be secured by means of a variety of licenses, many of which are described at www.gnu.org.

The concept of Free Software naturally extends to the more general and inclusive concept of Free Information, which of course is at the heart of the Freedom Digital Library. The FDL in turn springs from an idea suggested by Richard Stallman in an article posted on the Internet 5 February 2000.

There is an unavoidable ambiguity in the English word free, which has a double and confusing meaning in the present context. Free, as in Free Information, has nothing to do with cost, price, money, or value; and everything to do with freedom, liberty, unobstructed sharing, or sharability. "To understand the concept," as Stallman puts it, "you should think of 'free speech', not 'free beer.'"

Thus there is no inconsistency in the concept of selling or marketing for fiscal profit Free Information. But once one has bought an article of Free Information, or received it as a gift, generally it is wholly owned by the purchaser / recipient, to do with as he or she wishes; in much the same way the purchaser of a shovel or a rake from a hardware store is then the owner of the implement, and may use it, loan it to a neighbor, resell it, or give it away. The legal mechanism for securing this freedom for the purchaser / recipient / owner of Free Information is termed "copyleft," in distinction to copyright, which copyleft actually supplements.

The reason the legal mechanism of copyleft is necessary is that simply declaring a work to be in the public domain is not sufficient to secure its freedom. A work in the public domain may be modified slightly, copyrighted as a separate work, and wind up no less proprietary than an original copyrighted work. It may have been derived from, but is not itself Free Information, and it denies its recipients freedoms of use inherent to its source. Part of the definition of copylefted Free Information, in contrast, is that not only is the information itself Free: that same freedom is required to be passed on with all dirivative works. Copylefted Free Information cannot at some later evolutionary stage be converted into proprietary information.

Possibly the simplest example of copyleft would be a statement like the following:

[Title] Copyright © [yyyy Author's Name]
Verbatim copying and redistribution are permitted in any medium provided this notice is preserved.

Such a notice might be appropriate to a shorter work: an essay or a poem, which the author wishes to share freely, but without alteration. Longer works, or works the author wishes to circulate with greater or more explicitly defined freedom, may be copylefted by means of more complex terms of use.

A copyleft license we find applicable to a great variety of works that may find their way into the Freedom Digital Library is the GNU Free Documentation License (GFDL), which was originally designed to provide effective copyleft coverage to documentation for Free Software. And as already mentioned, numerous other copyleft, as well as some non-copyleft, non-free, licenses are available for study at www.gnu.org.

Different licenses are appropriate for different works, commensurate with the intention of the author; for it is you the author who ultimately decides the terms under which you will release your creative work to the public at large. There is a good deal more to be said about copyleft, some of which may be found here; and in Section 4.2. of the FDL Draft Vision Statement.