UBL, CII and EN 16931: the formats behind e-invoices
Most European e-invoices follow one standard, EN 16931, written in one of two XML languages.
One standard, two syntaxes
EN 16931-1 is the European standard for the content of an e-invoice: which pieces of information it has (invoice number, seller, buyer, VAT breakdown, amount due…) and what each one means. It defines them as business terms with numbers — BT-1 is the invoice number, BT-115 the amount due.
The standard does not prescribe one file format. The European Commission lists exactly two syntaxes that carry it: the UN/CEFACT Cross Industry Invoice (CII, XML schemas 16B) and UBL invoice and credit-note messages (ISO/IEC 19845:2015, which is UBL 2.1) — Implementing Decision (EU) 2017/1870. So the same invoice can arrive as UBL or as CII, and both are equally standard.
Specialisations: XRechnung, Peppol BIS and others
Countries and networks narrow the standard down for their use — a CIUS, a core invoice usage specification. Peppol BIS Billing 3.0 is one: OpenPeppol states that any document following it is always compliant with EN 16931. XRechnung is Germany's. A file says which one it follows in its specification identifier (BT-24).
Why this matters when you receive one
- Your accounting software reads the data, not a picture — so the XML is the invoice.
- Opening an XML file directly shows tags, not an invoice. A reader like this site turns the business terms back into a readable document, in your language.
- A copy of EN 16931-1 itself can be obtained free of charge from any national standards body that is a CEN member, as the Peppol documentation notes.
Facts on this page were checked against primary sources on 2026-10-21.