Wikipedia: Canonical URL’s

We have been looking into them over the past few months, and it really is a must for any websites which runs a eCommerce platform. Web stores selling multiple option products E.g. A T-shirt shop selling several different sizes, are at risk of duplicate content. Which means the T-shirt with five sizes will be read by each search engine five times and think you are trying to trick it into listing your site five times, this could result in your site being placed low in the search engine or even blacklisted.

Here’s your fix for this problem.
Our top three:

Magento – Magento canonical module
Drupal – Drupal canonical module
Wordpress -Wordpress canonical module