Canonical XML is important in part as an enabling technology for XML-Signature, which in turn is important as a means for digitally signing documents: contracts, documents used in electronic commerce, or messages of any kind whose internal integrity and authenticy it might be important to verify.

The announcement of the release of the Canonical XML Recommendation states that XML-Signature "already enjoys significant implementation", but the XML-Signature Working Group's Web site doesn't seem to provide any details at all about existing implementations of the technology.

The Canonical XML specification itself does not discuss application of the technology, but XML canonicalization of course has applications outside of digital signatures.

Note that the Canonical XML specification is also significant in that it was produced by a joint W3C/IETF working group.

Two XML documents which may not be byte-for-byte identical are said to be "logically equivalent" if their information content is the same, but they differ only in areas defined as insignificant by the XML specification, such as attribute ordering and use of certain whitespace. The Canonical XML specification defines an XML canonicalization algorithm for taking an XML document and generating a so-called canonical form of it that can be correctly compared, byte-for-byte, to canonical forms of other documents.

The canonical forms of any two logically equivalent XML documents will always be byte-for-byte identical. If a comparision of the canonical forms of two documents shows that they are not byte-for-byte identical, it indicates that the information content of the two documents is not logically equivalent; that is, the documents are not the "same thing".