Formats & standards
UBL vs CII: the two e-invoice XML syntaxes explained
UBL and CII are the two XML syntaxes that express the European e-invoice standard EN 16931. What each one is, where they are used (Peppol uses UBL; ZUGFeRD/Factur-X uses CII), and which one you actually need.
Last reviewed 2 June 2026
Once you start with structured e-invoicing you meet two acronyms (UBL and CII) and the question of which one to use. The short version: they are two ways of writing the same thing. Both express the European standard EN 16931; they just use different XML.
Two syntaxes, one standard
EN 16931 defines the meaning of an invoice; UBL and CII are two XML syntaxes that carry that meaning. An invoice in UBL and the same invoice in CII contain identical information, they are, in effect, two dialects of one language.
UBL
UBL (Universal Business Language, from OASIS) uses verbose, self-documenting element names, which makes it relatively readable. It is the syntax required by Peppol BIS Billing 3.0, and it is the dominant choice internationally for e-invoicing networks.
CII
CII (Cross Industry Invoice, from UN/CEFACT) is more compact and deeply nested. It is the syntax embedded inside the hybrid ZUGFeRD and Factur-X formats, and it is strong in the Franco-German market.
Which one do you need?
It depends on the channel, not on a personal choice. If you send over Peppol (for example into Belgium), you need UBL. If you produce a Factur-X / ZUGFeRD hybrid PDF (common in France and Germany), the embedded data is CII. Many systems and validators accept both, and good invoicing software handles the conversion for you.
Frequently asked questions
What is the difference between UBL and CII?
They are two XML syntaxes for the same European standard, EN 16931. UBL (OASIS) is verbose and used by Peppol; CII (UN/CEFACT) is compact and embedded in ZUGFeRD/Factur-X. The invoice content is equivalent.
Does Peppol use UBL or CII?
Peppol BIS Billing 3.0 uses the UBL syntax.
Which syntax is in a Factur-X or ZUGFeRD file?
The XML embedded in a Factur-X / ZUGFeRD hybrid PDF is CII (UN/CEFACT Cross Industry Invoice).
This guide is general information, not legal or tax advice. E-invoicing rules and dates change; always confirm the current position with the official source below or a qualified adviser before acting.
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