Wikipedia:Republishers

Republishers reproduce Wikipedia content wholesale in hard copy, usually for profit. The licensing terms may or may not be properly included in the publication. Publications that include some content from a Wikimedia project are not considered as republished.

Using these republishers on Wikipedia
Republishers are not reliable sources and not acceptable external links in articles per the verifiability policy. Articles that use a republished work as a source should be edited to either remove the work or to tag the source with {{Circular-ref}}. Leave {{backwardscopy}} on the article's talk page to identify Wikipedia as the original source.
Legality of republishing
Every contribution to the English Wikipedia has been licensed for re-use, including commercial, for-profit printing in hard copies. Republication is legal, so long as the licenses are complied with.
Effect of non-compliance with licenses
If the license is not complied with, then the republication is a copyright violation. You own the copyright to your contributions, not the Wikimedia Foundation. Legally, the Wikimedia Foundation is in the same position as the republishers (except that the WMF always complies with your license terms), because the WMF is republishing your copyrighted content under your license. If someone violates the terms of the license, then enforcement needs to come from the copyright owner. Consequently, complaints about violations need to be made by a person who actually wrote part of the improperly republished material.

Note: While some republishers do not even attempt to use properly issued ISBNs, noting those that do enables circular refs to be spotted more easily.