Creative Commons Licenses

All Creative Commons licenses are composed of three layers:

• The legal code (example) -- this makes the license enforceable in law. 
• The common deed (example) -- this is the human-readable license.
• Machine readable code that allows for searching and filtering by license.

[Image copyright 2011, Creative Commons, Nathan Yergler, Alex Roberts. Licensed to the public under CC BY 3.0 Unported] 

The four license elements make up the basis of the six different licenses (see below). 

	BY -  Attribution  This element applies to all CC license types. Credit must be given to the creator. Derivatives and adaptations are permitted.
	SA -  ShareAlike Users can redistribute, remix, adapt or otherwise alter the original material. Adaptations must be shared under the same terms.
	ND - No derivatives Users can copy or redistribute the material, even for commercial purposes, but no alterations, adaptations or derivatives are permitted.
	NC - Noncommercial Users can redistribute, remix, adapt or otherwise alter the original material for non-commercial purposes only.

A CC license, once applied to a work, is irrevocable, although a creator may choose to stop distributing the material at any point. The six license types are outlined in the table below. See the CC licenses page for more explanation of the licenses, including the deeds and legal code.

	Attribution BY - This exists on all license types. Credit must be given to the creator. Derivatives and adaptations are permitted. This is the least restrictive license.
	Attribution-ShareAlike BY-SA - Attribution required; derivatives and modifications are permitted as is commercial reuse. Reuse must be done under the same license terms.
	Attribution-NoDerivatives BY-ND - Attribution is required. Reuse is permitted, but if the work is to be shared, no alterations or modifications to the work are permitted.
	Attribution-NonCommercial BY-NC - Attribution is required. Derivatives and modifications are permissible, but only for non-commercial use.
	Attribution-NonCommercial-ShareAlike BY-NC-SA - Attribution is required. Derivatives and modifications are permissible, but only for non-commercial use. Reuse must be done under the same license terms.
	Attribution-NonCommercial-NoDerivatives BY-NC-ND - Attribution is required. Reuse is permitted but without alterations or modifications and only for non-commercial use. This is the most restrictive license.

In addition there are two public domain tools one can apply to works.

	The public domain tool, also known as CC 0 (CC-zero) indicates "no rights reserved." Creators can use this tool to freely give the content to the public domain; creators have waived all  copyright on materials with this designation.
	The public domain mark can be used on works that you know are free of known copyright restrictions. Use this mark cautiously as materials may still have copyrights in other jurisdictions.