In all reality there may be several versions:

http://yourdomain.com

http://www.yourdomain.com

yourdomain.com/

So you probably have links pointing from other web sites to your web site. If they are all pointing at different versions of the URL then you may be missing out on “link juice.” Those links are valuable when it comes to SEO and it’s important that they all point back to one domain. Otherwise you are sharing you “link juice” amoung several domains.

So how do you tell Google and the other search engines that you only want to refer to one domain?  With a 301 redirect written in your .htaccess file. It’s easier than it sounds. If you already have one then just add this to it. But if you have no .htaccess file just create one using your favorite text editor. Be sure to save it as an .txt file.

So if you want to redirect all of the non-www traffic to the www.domain name you would use the following just substitue your domain name where indicated:

Options +FollowSymLinks 
RewriteEngine on 
RewriteCond %{HTTP_HOST} ^yoursite.com [NC] 
RewriteRule ^(.*)$ http://www.yoursite.com/$1 [L,R=301] 

As with any change to your domain always test it once it has been uploaded to make sure it is working properly.