A canonical link is an HTML element that helps to prevent duplicate content issues by indicating the canonical or so called “desirable” version of a web page as the part of search engine optimization. Duplicate content is a serious issue. It is a term that is used in order to describe the content which appears on more than one web page. It is used in the field of a search engine optimization. When the multiple web pages contain the same content, Google or other search engines can penalise or cease showing this site in any relevant search results. When the site contains the multiple sub domains such as with or without “www”, the duplicate content issues can arise too. Malicious duplicate content is a tool which is used for making some pressure on, manipulating search results and gain more traffic. It is called as search spam. In February Google, Yahoo and Microsoft declared the support for the canonical link element which can be inserted into the <head> section of the web page in order to allow avoiding the duplicate content issue. Please examine the examples of the canonical link element carefully: <linkrel="canonical"href="http://example.com/"/> <linkrel="canonical"href="http://example.com/page.html"/> Of course, it will take you much time to create canonical link elements manually, but you can use the special third party extensions to make it easier and automatically. For example, if you are a Magento user and you have a Magento site. One of the fresh Magento extensions that is being developed at the moment is GoMage SEO Booster. One of the useful features of this significant Magento extension is that the plug-in adds Canonical URL Meta Header to your pages. It saves your site from being penalized by the search engines such as Google, Yandex, Yahoo and so on.