You’ll more than likely of heard of URL canonicalization, particularly “Google URL canonicalization issue” but what is it, and what do you need to do about it?
It’s a big word used by Americans, they like big words, especially at Google, makes them sound all clever! (well, they are clever, so we’ll let them off)Â 
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Canonicalization simply means making something canonical, and canonical means (According to the dictionary)Â “conforming to accepted principles or standard practice.”
So basically URL canonicalization just means URL standardizing.
The most common requirement for URL canonicalization is with the home page.
For instance you could link from your pages to “site.com” or “www.site.com” or “www.site.com/index.htm” an so on – quite a number of options.
It doesn’t really matter which you choose, what matters is that you standardize, in other words pick one & stick with that consistently throughout your navigation.
You can 301 re-direct the other URL’s to the one you decide to make standard, so that if someone types into their browser “website.com” they’re re-directed to “www.website.com” this is good practise, it’s not crucial though – so don’t be too concerned with it. It’s one of those things that is definately a good idea in theory, and is certainly likely to help rather than hinder – but it’s very unlikely to make any huge difference.
So, if you’re concerned about URL canonicalization, just make sure you pick onr form of URL & stick to that as the standard – and if you want to be sure you pull out all the stops, then also use a 301 re-direct to redirect the other options to the URL that you choose to make the standard.
For more info see the Matt Cutts Blog
