From Wikipedia on 24-Feb-2013
URL: http://en.wikipedia.org/wiki/Wikipedia:Reusing_Wikipedia_content
Wikipedia
Wikipedia’s text content, in a nutshell, can be used under the terms of the Creative Commons Attribution Share-Alike license (CC-BY-SA); unless otherwise indicated, it can also be used under the terms of the GNU Free Documentation License. The global terms of use dictate the ways content from Wikimedia sites can be properly attributed when used under the CC-BY-SA license. The GFDL imposes different requirements, which are dictated in the text of the license. The English text of these licenses is the only legally binding document; what follows is our interpretation of how material may be reused under them.
Re-use of text under Creative Commons Attribute Share-Alike
Attribution
To re-distribute a text page in any form, provide credit to the authors either by including a) a hyperlink (where possible) or URL to the page or pages you are re-using, b) a hyperlink (where possible) or URL to an alternative, stable online copy which is freely accessible, which conforms with the license, and which provides credit to the authors in a manner equivalent to the credit given on this website, or c) a list of all authors. (Any list of authors may be filtered to exclude very small or irrelevant contributions.) This applies to text developed by the Wikipedia community. Text from external sources may attach additional attribution requirements to the work, which should be indicated on an article’s face or on its talk page. For example, a page may have a banner or other notation indicating that some or all of its content was originally published somewhere else. Where such notations are visible in the page itself, they should generally be preserved by re-users.