Key takeaways
- The CII format (UN/CEFACT Cross Industry Invoice) is one of the two syntaxes allowed by the EN 16931 standard, alongside UBL 2.1.
- CII and UBL 2.1 express the same invoice semantic model: same information, different XML grammar.
- For billing on Peppol, the syntax exchanged in practice is UBL 2.1; CII appears mostly cross-border and in hybrid formats.
- Compliant software spares you writing any XML: the CII format matters mostly when receiving a foreign invoice.
The CII format, the second syntax of the European e-invoice
The European e-invoice does not have a single technical form. Behind the EN 16931 standard, two XML syntaxes officially coexist: UBL 2.1, the most widespread in Belgium, and the CII format, short for Cross Industry Invoice. Both are allowed, both are valid, and telling them apart avoids a common confusion when a received file does not look like what your software issues.
This duality is written into EU law. Commission Implementing Decision (EU) 2017/1870 of 16 October 2017 publishes the reference to EN 16931 and its list of syntaxes under Directive 2014/55/EU. That list retains exactly two syntaxes: the UBL messages (invoice and credit note) and the UN/CEFACT CII message.
This article explains what the CII format is, how it differs from UBL without changing the content of the invoice, and in which cases a Belgian business actually meets it. For the syntax most common here, read The UBL 2.1 format explained; for the model common to both, The EN 16931 standard.
Two syntaxes, one semantic model
The point to remember is that CII and UBL do not conflict on substance. They express the same semantic model defined by EN 16931: the seller, the buyer, the invoice lines, the VAT breakdown and the monetary totals are all there, identically. What changes is the XML structure and the tag names.
A single piece of data, for instance the total amount due, carries a different path and label depending on the syntax. Software that knows only one syntax will not read the other, even though the information is the same. That is why compliance with EN 16931 means being able to handle both sides.
| CII format | UBL 2.1 | |
|---|---|---|
| Expresses the EN 16931 semantic model | ||
| Covers the invoice and the credit note | ||
| Published by UN/CEFACT | ||
| Published by OASIS (ISO/IEC 19845) | ||
| Syntax exchanged in practice on Peppol for billing |
Where the CII format comes from
The CII format is maintained by UN/CEFACT, the United Nations Centre for Trade Facilitation and Electronic Business. It belongs to a family of standardised messages designed for exchanges between businesses in different sectors, hence the name Cross Industry Invoice. The syntax rests on the XML schemas published by UN/CEFACT.
UBL, for its part, is published by the OASIS consortium and standardised under the reference ISO/IEC 19845:2015. The two syntaxes therefore come from distinct bodies and different histories, which is why they coexist rather than one having replaced the other. EN 16931 reconciles them at the semantic level without merging them.
allowed syntaxes
UBL 2.1 and UN/CEFACT CII
implementing decision
(EU) 2017/1870 publishing EN 16931
semantic model
common to both syntaxes
Where the CII format actually appears
In Belgium, for the B2B e-invoicing mandate, the invoice travels over the Peppol network in the Peppol BIS Billing 3.0 profile, which is built on UBL 2.1. In that setting, you do not issue CII. The CII format does not disappear for all that: it remains present in several contexts your software must be able to handle.
The contexts where the CII format appears
Cross-border exchanges
A partner established in a country where CII is favoured may send you an invoice in that syntax.
Hybrid PDF + XML formats
Formats such as Factur-X embed an XML file in the CII format inside a human-readable PDF.
European public procurement
Directive 2014/55/EU requires the public entities in scope to receive and process both syntaxes.
Certain business software
Some ERP systems and legacy platforms natively produce CII rather than UBL.
The practical rule is asymmetric. When issuing, in Belgian B2B, you produce UBL via Peppol. When receiving, you may get either UBL or CII, and your tool must interpret both without asking you to step in.
Compliant invoices, whatever the syntax
YouInv generates your invoices in the Peppol BIS Billing 3.0 profile and sends them over the Peppol network, without you touching the XML.
What it changes for your business
The good news echoes that of UBL: you do not have to handle the CII format by hand. Compliant software produces the right syntax when issuing and decodes the other when receiving. Your job is limited to entering correct data and choosing a tool able to handle both.
What changes is the selection criterion. Software that read only UBL would expose you to rejecting a valid invoice received in the CII format. Before choosing or updating your solution, check that it covers the two syntaxes allowed by EN 16931, both when issuing and when receiving.
Further reading
- The UBL 2.1 format explained: the most common syntax in Belgium, in detail.
- The EN 16931 standard: the semantic model common to both syntaxes.
- Peppol BIS Billing 3.0: what the format contains: the profile exchanged on the Peppol network.
The reference source is authoritative: Commission Implementing Decision (EU) 2017/1870 published in the Official Journal of the European Union.
What is the CII format?
The CII format (UN/CEFACT Cross Industry Invoice) is an XML e-invoice syntax published by UN/CEFACT. It is one of the two syntaxes allowed by the European standard EN 16931 to express the semantic model of the invoice, the other being UBL 2.1.
What is the difference between the CII format and UBL 2.1?
CII and UBL 2.1 are two different XML grammars that express the same EN 16931 semantic model. The same information (seller, buyer, lines, VAT breakdown, totals) is present in both, but written with tags and a structure specific to each syntax. Compliant software must be able to read both.
Is the CII format used on the Peppol network?
For billing, the Peppol network uses in practice the Peppol BIS Billing 3.0 profile, built on the UBL 2.1 syntax. The CII format is allowed by EN 16931 and appears mostly in cross-border exchanges and in hybrid formats, but it is not the syntax exchanged by default on Peppol.
Does a Belgian business need to master the CII format?
No. For the Belgian B2B mandate, the invoice travels over Peppol in the Peppol BIS Billing 3.0 profile (UBL 2.1). Compliant software generates and validates that format without you writing any XML. The CII format matters mostly on receipt, when a foreign partner sends an invoice in that syntax.
Why does EN 16931 allow two syntaxes?
Commission Implementing Decision (EU) 2017/1870 publishes the reference to the EN 16931 standard and its list of syntaxes under Directive 2014/55/EU. Two syntaxes are retained, UBL 2.1 and UN/CEFACT CII, to account for the ecosystems already in place across Europe and avoid forcing a rebuild on everyone.
