How do I redirect non-WWW traffic to WWW?

To set up this permanent WWW redirect you need to add the following lines to your site's .htaccess file:

RewriteCond %{HTTP_HOST} *!^www*.yourdomain\.com [NC]
RewriteRule (.*) http://www.yourdomain.com/$1 [L,R=301]

* Please replace "yourdomain.com" with your actual domain name and its extension.