UBL 2.1 E-Invoice Standard

Universal

OASIS Open · Version 2.1

UBL 2.1 is a generic XML invoice format developed by OASIS for international use. It is the technical syntax layer on which Peppol BIS 3.0 is built. While Peppol BIS constrains UBL for e-invoicing, UBL 2.1 can be used directly for cross-border B2B transactions.

3 Countries

46+ Data fields

Yes Structured format

Varies Delivery network

AI Summary

UBL 2.1 is the foundational XML syntax for e-invoicing used by the Peppol network. It predates EN 16931 and Peppol BIS, and serves as the technical implementation layer. While Peppol BIS 3 constrains UBL 2.1 for e-invoicing use cases, the underlying UBL standard also covers purchase orders, catalogues, and other business documents. Many countries (Belgium, Netherlands, UK) accept UBL 2.1 as a compliant format.

Grounded in official sources listed below. Not a substitute for legal or tax advice.

Quick Answers

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Key Data Fields

The following data elements are central to the UBL 2.1 specification. Mandatory fields are required for compliance; optional fields add detail.

Invoice Header

Code Field name Mandatory

cbc:ID Invoice number Yes

cbc:IssueDate Issue date Yes

cbc:DueDate Due date No

cac:AccountingSupplierParty Seller Yes

cac:AccountingCustomerParty Buyer Yes

Validation Requirements

Invoices using this standard must pass the following validation checks before transmission. Rejections typically occur due to missing mandatory fields or incorrect data types.

Must conform to UBL 2.1 XSD schema
All UBL-required elements must be present
Country-specific extensions may apply

Key Advantages

International standard with broad adoption
Open and royalty-free
Used as the basis for Peppol BIS 3
Covers more than invoices (orders, catalogues, etc.)

Implementation Considerations

Large schema — many optional elements that confuse implementers
Requires Peppol network or custom integration for delivery
Less constrained than Peppol BIS — more room for interoperability issues

Common Mistakes to Avoid

Not understanding that UBL 2.1 is a generic format — Peppol BIS adds necessary constraints
Missing required party identification elements

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Official Sources

All information on this page is based on the sources listed below. Always verify current requirements with the issuing authorities.

OASIS UBL 2.1 Specification Standard Body

OASIS Open Last verified: 2026-05-01

Official UBL 2.1 specification; invoice and related document schemas