edit Kristina Weis on August 19, 2010
edit Is your website turning away would-be visitors?
Though websites often live at web addresses that start with www - like http://www.Example.com - it's increasingly common for people to type just Example.com into the navigation bar of a web browser.
Most webmasters make sure that typing either "www.Example.com" or "Example.com" into the navigation bar will get someone to the right website. Too often, however, people don't think about this issue, and someone who types just "Example.com" won't get to the website at all. Worse yet, that person may assume that the website and business no longer exist.
Wait, it gets even worse. Any links to your website that don't include "www." - and we all want valuable inbound links, don't we? - won't work either, and won't take people to your site when they click them.
edit Point People to Your Website with a Redirect
To make sure that both http://www.Example.com and http://Example.com take people to your website, the recommended method is to create a redirect from http://Example.com to http://www.Example.com. Of note, webmasters need to make sure that http://Example.com resolves to some IP address before they can add a redirect.
The best method is to create a 301 redirect, also known as a "Moved Permanently" redirect. This is the recommended solution because it means that your website's content lives in just one place. That means any search engine optimization (SEO) tactics you use won't be diluted by directing the engines -- and people -- to two different places.
Links from blogs or news sites to your home page, for example, will go to just one page, not to two. That means the power of those links all concentrates on just the one page, giving you better PageRank, and making your home page come up higher in search results. Splitting the goodness of those links to two pages could mean that neither will rank very well.
You can read more about why it's not a good idea to duplicate your website at both http://www.Example.com and http://Example.com in Ian Lurie's article about canonicalization. Now there's a word you don't get to see every day!
For technical guidance on creating a 301 redirect, see this article at TutorialsRoom.com. Unless you're a very technical person though, you will probably want to ask your hosting company or the person or company that set up your website to put the 301 redirect in place to fix this issue.