Large search engines attempt to filter their search results by removing any results that duplicate the content of other search results. Such filtering is referred to as "duplicate content penalty". It is important to understand and identify what "duplicate content" actually is. Duplicate content is generally defined as substantive blocks of text that are copied from one site to another. Some webmasters try to use duplicated content in an attempt to manipulate and influence search engine rankings. The search community still occasionally debates the legitimacy and existence of duplicate content filters, but whether they exist today, or will exist tomorrow, is really irrelevant. Most webmasters have simply accepted the fact that the duplicate content penalty is currently enforced by at least some of the major search engines. With that in mind, how does the search engine determine which version of the content is the original, and which is duplicated? It is difficult for the search engine to tell which website is responsible for the original version of any content, and some innocent websites might find themselves penalized or banned for including duplicated content. After analyzing the behavior of search engines, it is safe to assume that the search engines will often retain the content listing from what it considers to be the most 'trusted' source. They may look at the number of incoming related links, the age of the domain, or any other SEO factors that reinforce the reputation of the domain that contains the duplicated content. If one of the 'copies' is considered by the search engine to be from a reputable source, they my find themselves ranking well, while the actual source of the 'original' version may find themselves unjustly banned or penalized. Representatives from the major search engines have all made it clear that they prefer search engines that contain unique content. Webmasters who want to avoid any current or future bans will do well to follow these simple guidelines in order to avoid duplicate content penalties: 1. Redirects If you redesign your website, use permanent 301 redirects. Redirects are a legitimate way of routing web traffic. 2. Unique Each page within a website should be unique. The focus of each page on a website, even if it's similar to the theme of another page, must contain unique and original content. 3. Multi-Language If there are multiple language versions of a website, consider using a different domain for different versions; search engines do not view an article translated into a variety of foreign languages as being duplicated content -- each language version is unique content in the eyes of the search engine. 4. Unique Meta Tags Each web page should contain unique meta tags. 5. Robots.txt If you do have intentional duplicate content on your website, be sure to have a "robots.txt" file for your site to prevent the search engines from indexing the areas with duplicated content (or any areas of the website that you wish to remain private, for that matter). 6. Affiliate Twist If you are promoting products or services using an affiliate program, use unique and distinctive product descriptions and web copy. If you simply use the same descriptions provided by the product owner or service provider, it's very likely that your copy could be viewed as duplicated content. 7. Copyright Include a copyright notice on your website. 8. Enforce If you discover that another website is scraping your unique web content and replicating it, enforce your copyright! Use CopyScape at http://www.copyscape.com/ , or use their "copy sentry" service to receive notification of any infractions. If you discover a copyright violation, contact the website and politely request appropriate changes. If the changes are not made in a reasonable and satisfactory amount of time, contact the ISP (web host) of the infringing site, and file a DMCA complaint with Google http://www.google.com/dmca.html . 9. Avoid Identical Content Do everything you can to avoid serving a web page that contains content identical or closely related to another page. If for some reason you have two pages that contain identical content, use a robots.txt to block the search engines from spidering one version of the page. Other Tools: Duplicate Page Checker - http://www.webconfs.com/similar-page-checker.php While it may still be debatable whether all the major search engines currently employ a duplicate content penalty, all have made it abundantly clear that they do not have any desire to provide search results that rehash the same content over and over. Actively avoid any potential penalties by taking a proactive approach to building unique content.