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Actually, canonical tags are the absolute last-ditch way of dealing with this issue. The correct solution is to use 301-redirects to force all version of the URL except the primary to redirect to the primary (also called canonical) URL. Canonical in this instance just means the primary or most authoritative version of something. Nothing to do with the tags of the same name. The only reason to use the rel=canonical tag for this is if you have absolutely no way to do it through 301-redirects. (For instance your host doesn't allow access to the .htaccess file and your DNS system doesn't allow it either.) Use Travis's info below for exactly how to do this in .htaccess. There are also many other posts here in Q&A that address this if you want more reference points. Paul