CIUS
Core Invoice Usage Specification. The official EN 16931 mechanism for constraining the norm into a national or sector-specific variant — without stepping outside it.
Definition
A CIUS (Core Invoice Usage Specification) is a profile of EN 16931 defined by CEN/TR 16931-6 (methodology). Principle: a CIUS can restrict EN 16931 but never extend it. Concretely, a CIUS:
- May remove EN 16931 optional elements that the variant does not use.
- May require conditional elements of the norm.
- May constrain allowed values (e.g. only certain country codes, certain VAT codes, certain allowance reasons).
- May add business rules (Schematron) that tighten those of EN 16931.
- Can never add a field that the norm does not define.
Beside CIUS, EN 16931 also accepts extensions (CEN/TR 16931-7) — but these go outside the normative scope and break default interoperability. The European doctrine pushes for staying within CIUS wherever possible.
Origin
The CIUS concept was introduced in 2017 with EN 16931's publication, to address member states wishing to adapt the European invoice to their own fiscal and regulatory framework. CEN/TR 16931-6 published in March 2018 formalised the methodology. Several CIUS coexist in 2026: PEPPOL BIS Billing 3.0 (OpenPEPPOL), Factur-X (France), XRechnung (Germany), FatturaPA (Italy), UBL.BE (Belgium), Faktura SI 2.0 (Slovenia).
Example in context
XRechnung is a CIUS of EN 16931 used for B2G invoicing in Germany. It restricts, relative to the norm: it mandates Leitweg-ID (BT-10) as the routing identifier, it restricts country codes to ISO 3166-1 alpha-2 format, it prohibits some invoice sub-types of little use in the German context. An XRechnung invoice is by construction a valid EN 16931 invoice. A German PEPPOL Access Point can route it without transformation.
Related terms
- EN 16931 — the norm CIUS restricts.
- PEPPOL BIS Billing 3.0 — the most-deployed CIUS.
- CEN — the CIUS methodology editor.
- Leitweg-ID — the German extension referenced by XRechnung.