In short
An electronic invoice is a structured file that software can read. Three names come up all the time: UBL, CII and Factur-X. UBL and CII are two XML syntaxes: two ways of writing the same invoice data. Factur-X is a file format: a PDF that carries a CII file inside.
One standard for the content
The European standard EN 16931 defines what an electronic invoice contains: the seller and the buyer, the lines, the VAT, the totals, the payment terms. It says nothing about the file format. It does recognize two XML syntaxes that can carry that content:
- UBL (Universal Business Language), published by OASIS. It is the syntax of the Peppol network.
- CII (Cross Industry Invoice), published by UN/CEFACT.
Both can express the same invoice. Their elements are organized and named differently, so an invoice written in one syntax can be rewritten in the other without losing what EN 16931 describes.
Factur-X
Factur-X is a hybrid invoice. A person opens a readable PDF (PDF/A-3), and software reads the invoice data attached to it as an XML file in CII syntax. The German standard ZUGFeRD is the same format. Factur-X defines several profiles, from Minimum to Extended: the EN 16931 profile carries the full content of the standard, and the Extended profile adds more. For the French e-invoicing reform there is a dedicated profile, EXTENDED-CTC-FR, a subset of EXTENDED.
At a glance
| Name | What it is | Where you meet it |
|---|
| EN 16931 | The content of an e-invoice, whatever the file | The common base of the others |
| UBL | An XML syntax (OASIS) | The Peppol network |
| CII | An XML syntax (UN/CEFACT) | Inside Factur-X, and XML exchanges |
| Factur-X | A PDF with a CII file inside | France, and Germany as ZUGFeRD |
| EXTENDED | The Factur-X profile with more fields than EN 16931 | Complex invoices |
| EXTENDED-CTC-FR | The French profile for the reform, a subset of EXTENDED | France |
Which one will you meet?
It depends on who sends the invoice and through which channel. The Peppol network carries UBL. A PDF invoice that contains data is usually Factur-X or ZUGFeRD. Systems that exchange XML directly use UBL or CII. In France, the e-invoicing reform recognizes the three formats Factur-X, UBL and CII; the formats and their profiles are defined by the AFNOR standard XP Z12-012 (specifications published on impots.gouv.fr).
Which one should you use?
Most of the time you do not choose: your customer, your invoicing platform or your ERP does. If you have a choice, use the one your software and your customers already handle, and ask them which profile they expect. Many companies need to read both syntaxes, which is why conversion exists.
What a converter does
A converter reads the invoice in one syntax, maps it to the EN 16931 model and writes it in the other syntax. It does not change the amounts or the parties. It cannot invent data that the other syntax requires but the source did not contain, and information that goes beyond EN 16931 (the extension fields of a profile such as Extended) may not all have an equivalent.
Check a converted invoice before you send it. The checklist lists what to compare.
Last updated: 2026-10-19