Well there is a bunch of standards aimed at this, already mentioned are EDI and cXML. But another very ambitious is Oasis' UBL. In Denmark and a few other european countries you basically have to support invoicing in UBL (Or more specifically the danish subset OIOUBL or scandinavian subset NESUBL) if you want to do business with government as it is a requirement.[1] In a transition-phase (which i don't know if still is ongoing) suppliers could send invoices to a "scanning agency" that would attempt to convert the invoice to OIOUBL and send on to the government institution.
This has pushed adoption of these things in Denmark quite a bit and we see a lot of big corporations demanding of their suppliers that they support these formats.
This has pushed adoption of these things in Denmark quite a bit and we see a lot of big corporations demanding of their suppliers that they support these formats.
Edit: [1] Previous to OIOUBL danish government had its own format called OIOXML: http://en.wikipedia.org/wiki/OIOXML