There are hundreds of sources explaining this, but whenever you need one, you can't find a matching one , so I'll repost my sample…

The goal: redirect NON-www addresses the corresponding WWW-address to make sure search engines and users always use the correct one and don't put you under some SE penalties.

E.g. professional-pm.com should redirect to www.professional-pm.com

This instructions applies to Apache, using mod_rewrite commands

• Step 1 : create a simple file called ".htaccess"

• Step 2 : fill the following in you file

Of course replace "professional-pm.com" with your domain name.

• Step 3 : AFTER CHECKING if there are no other .htaccess files there ( then you should add the RewriteCond part only to those) upload that file into your web server's root (e.g. public_html ) and you should be done, unless your web host has disabled mod_rewrite for some reason…