When writing wiki articles, we sometimes want to use material that is copyrighted ("all rights reserved" or under an incompatible license). In these cases we must at least paraphrase the material, to avoid violating the copyright.
How far do we have to go? It's useful to know that under the laws of many countries, copying one or two sentences is not considered to be a copyright violation. The United States has a "fair use" exception in its copyright law which applies to uses such as these. Some other countries, even if they lack a general "fair use" or equivalent exception, may have more specific exceptions such as a quotation right (though this is often subject to conditions, such as that the quotation be made for a "legitimate" purpose such as criticism, review or reporting the news). Furthermore, short quotations from a longer work may in some cases not legally amount to an act of copying at all, because a "substantial part" of the original has not been taken..
A good guide for a wiki article then, is that if you want to use more than this in a single wiki page, then it should be kept short and clearly marked as a quote (in which case it may be legally permissible). Unless there is a specific reason for quoting a source, it is usually better to rewrite the text, and integrate it with the article as a whole. In this case, references are used only for the reader to be able to verify the accuracy of the information.
- Hawkes & Son (London) Ltd v Paramount Film Service Ltd  1 Ch 593
- Fair Use: Interpretations and Guidelines - The Fair Use Doctrine Part II by Lloyd L. Rich, 1996, The Publishing Law Center