Belgium has rolled out a series of e-invoicing mandates, first requiring businesses to submit structured e-invoices when dealing with public sector entities and soon expanding to B2B transactions from January 2026. These mandates rely on compliance with the EN 16931 standard, ensuring that invoices follow a common, machine-readable structure that both sender and receiver systems can understand without human intervention.

In this article, we’ll explore EN 16931, why it matters for Belgium’s digital economy, how it works in practice, and what businesses need to know to stay compliant and competitive in this new era of standardized e-invoicing.

E-Invoicing, Standardization and EN 16931

As businesses and governments worldwide move towards digital transformation, electronic invoicing (e-invoicing) has become a cornerstone of modern financial operations. Unlike traditional paper or PDF invoices, e-invoices are structured digital documents that can be automatically generated, transmitted, received, and processed by accounting systems — dramatically improving efficiency, accuracy, and speed. By replacing manual data entry with seamless machine-to-machine communication, e-invoicing reduces costs, minimizes errors, and supports faster payments.

Recognizing these advantages, the European Union took a major step by introducing legislation to promote standardized e-invoicing across member states, particularly in public procurement. A key result of this effort is the EN 16931 standard a European framework that defines the essential data elements of an electronic invoice and ensures interoperability between different businesses and public authorities across borders.

Introduction to EN 16931: Europe’s E-Invoicing Standard

EN 16931 is the official European standard for electronic invoicing. (EN stands for “European Norm.”) It was published in 2017 by the European Committee for Standardization (CEN) to harmonize e-invoices across Europe. The full title is “Electronic invoicing – Semantic data model of the core elements of an electronic invoice.”

Simply put, EN 16931 defines:

• What information every e-invoice must include.
• How that information should be structured for uniform understanding across systems.

Why Was EN 16931 Created?

EN 16931 was developed in response to the EU Directive 2014/55/EU, which required all public authorities in EU member states to:

• Accept and process e-invoices in a common format.
• Facilitate cross-border procurement by ensuring that invoices could be exchanged seamlessly across different EU countries.

The Core Invoice Model

At the heart of EN 16931 is the core invoice model — a standardized list of all essential pieces of information that ensures the fundamental business data in any invoice remains consistent, complete, and interoperable across different systems and countries. such as:

• Seller’s name
• Buyer’s address
• Invoice date
• Tax amount
• And more

EN 16931 as a Semantic Standard

EN 16931 is often referred to as a semantic standard because it focuses on:

• The meaning of data elements (e.g., what "Invoice Issue Date" or "VAT Amount" actually represents).
• Rather than enforcing one specific technical format.

This approach allows flexibility in how the data is technically implemented, while still ensuring that everyone interprets the information the same way.

How EN 16931 is Implemented: Technical Formats

Although EN 16931 defines the content and meaning, it must be implemented through specific technical formats (also known as syntaxes). The two primary approved formats are:

• UBL (Universal Business Language) – XML-based structure widely used in e-commerce and government procurement.
• UN/CEFACT’s CII (Cross Industry Invoice) – Another XML standard developed for broad international business use.

These formats structure the invoice data according to EN 16931’s rules, enabling automated processing by IT systems.

Impact: A Common Language for E-Invoices in Europe

Thanks to EN 16931 all EU countries now use a common invoice language for public procurement and Cross-border interoperability has dramatically improved.

Businesses can send structured invoices across Europe without worrying about national format differences, simplifying public sector transactions and reducing administrative burdens.

Beyond Compliance: EN 16931 as a Foundation

EN 16931 is not merely a bureaucratic checkbox. It serves as a foundation for many e-invoicing systems and networks. For instance, the Peppol network an international e-invoicing infrastructure builds its invoice format to comply with EN 16931.  This broad adoption means EN 16931 is a critical pillar in building unified, efficient, and digital trade ecosystems across Europe and increasingly, worldwide.

Key Features of EN 16931

How EN 16931 Works? 

Suppose a small business in Belgium needs to send an invoice to a government agency. Here's how the process might work step by step:

1. Invoice Creation: The business uses e-invoicing software (or an online portal) to create the invoice. Instead of producing a PDF, the software will generate the invoice data in a structured format that follows EN 16931 rules. Essentially, the software fills in all the required fields (like buyer, seller, amounts, tax details) into an electronic invoice file (often an XML file conforming to the EN 16931 data model).
2. Sending the Invoice: The electronic invoice file is then sent through an e-invoicing network or platform. In Belgium, for example, many suppliers use the Mercurius platform, which is a government-provided “mailroom” for e-invoices​. Mercurius is connected to the Peppol network, an international e-delivery network for business documents. The idea is that the supplier’s system hands off the EN 16931-compliant invoice to the network, rather like dropping a letter in a postal system, but entirely digital. This network knows how to route the invoice to the right recipient (the government agency’s system), because participants are registered/addressed in the network.
3. Delivery and Receipt: The government agency’s financial system, which is set up to receive EN 16931 invoices, gets the file through the network. Thanks to standardization, the file is immediately understood by the agency’s software – it can automatically recognize the invoice number, the amounts, the VAT details, etc., because everything is labeled and structured in the expected way. There’s no need for a person to retype the info; the data can be automatically checked and entered into their accounts payable system.
4. Processing and Payment: Once received, the agency can process the invoice quickly – automated validations can check that the numbers add up (for example, that the tax rates match the amounts) and that required information is present. Because the invoice was transmitted through a secure network and in the expected format, authenticity and integrity are assured (often with digital signatures or network security measures). The agency can then approve the invoice and schedule payment. The supplier might even get an electronic confirmation or status update (e.g., invoice accepted) through the system, providing end-to-end transparency.
5. Archiving: Both sender and receiver can store the invoice electronically for record-keeping. Since it’s already structured data, it’s easy to search, sort, and audit if needed.

Explanation:

Throughout this process, EN 16931 is the common language that both the supplier’s and buyer’s systems understand, while Peppol (in this example) is like the delivery infrastructure. The result is a smooth, fast transaction: the invoice goes from the supplier’s computer to the buyer’s system without any manual intervention.

 In real life, this means invoices get paid faster and with fewer mistakes. For instance, Belgium’s Mercurius platform (which uses EN 16931-compliant formats) even offers a feature to convert the data into a PDF for human readability if needed​=, ensuring that even parties without advanced software can review the content. But the key is that in the background, the data remains standardized and machine-readable. 

This simple example shows how EN 16931 makes e-invoicing efficient: senders don’t have to worry about each customer’s format requirements, and receivers can process many invoices automatically, saving time and money.

Structure and Components of EN 16931

What does an EN 16931 e-invoice look like (in terms of information included)? At a high level, it contains all the details you would expect on a standard invoice, but organized in a structured way.

The standard defines a set of data fields and groups that cover the necessary invoice information. Here are the key components of an EN 16931-compliant invoice:

• Header Information: Basic invoice metadata, such as a unique invoice number, the invoice date, and the type of invoice (for example, whether it’s an ordinary invoice or a credit note). It also includes references to related documents (like a purchase order number) if applicable.
• Seller (Supplier) Details: Information about the entity issuing the invoice. This includes the seller’s name, address, and tax identifiers (for example, VAT number in Europe). It may also include contact info like email or phone, and the seller’s bank account details for payment.
• Buyer (Customer) Details: Information about the invoice recipient. This typically has the buyer’s name, address, and possibly a tax ID or business registration number. In B2G invoices (business-to-government), it might include specific identifiers for the public entity or references like a public contract number.
• Invoice Line Items: A list of line-by-line details for each product or service being billed. For each line, the invoice will specify a description of the item/service, the quantity (or duration, if a service), the unit of measure (e.g., hours, pieces), the unit price, and the line amount (quantity × unit price). Each line can also have information on applicable taxes for that item and any discounts or allowances on that line.
• Tax Details: A breakdown of taxes applied to the invoice. In countries with VAT (like Belgium), for example, an EN 16931 invoice will clearly state the tax rate (e.g., 21% VAT) and the tax amount for each rate used. If multiple tax categories apply (say one item at 6% VAT and others at 21%), the invoice data will segregate the amounts per category. It also handles other tax types or exemptions by providing codes to specify the reason (for instance, if an item is tax-exempt or reverse-charged, the relevant code and explanation can be included).
• Totals and Summaries: The invoice will calculate totals such as subtotal (net amount) before tax, total tax amount, and grand total (gross amount) payable. It will also specify the currency (e.g., EUR for euros). These totals are crucial for both parties and are always explicitly present in the structured data so that there’s no confusion.
• Payment Terms and Information: Details on how and by when the payment should be made. This can include the payment due date, accepted payment means, banking information (like IBAN for the seller’s bank account), and any early payment discount or late payment penalty terms.

Explanation: 

All these components are defined in EN 16931’s semantic data model. In fact, the standard defines hundreds of specific data fields to cover various scenarios and business needs (many fields are optional or conditional). 

For example, EN 16931 includes elements for things like the buyer’s purchase order reference, the delivery address (if different from the billing address), or an allowance on the whole invoice (like a 5% discount on the total)​.  Each field has a defined meaning and format – for instance, dates must be in a certain format (YYYY-MM-DD) and amounts must clearly indicate their currency. By specifying these details, EN 16931 ensures that whether an invoice is issued in Belgium, France, or any other country, the core information is structured the same way and carries the same meaning. 

This comprehensive structure covers everything needed for legal and tax compliance as well. (For instance, EU VAT laws require certain info on invoices; EN 16931 makes sure all those elements are present and labeled.)

Key Requirements of EN 16931 Compliance – Summary

EN 16931 compliance means your e-invoice is complete, correctly structured, validated, and universally readable by any compliant system in the EU. Most businesses achieve this by using certified e-invoicing software that automatically applies all the required rules and checks.

To comply with the EN 16931 standard for electronic invoicing, both the e-invoice and the systems that create or receive it must meet the following essential requirements:

Benefits of EN 16931 Compliance

EN 16931 compliance brings significant advantages for businesses and public entities adopting standardized electronic invoicing across the EU:

• Seamless Cross-Border Trade: Invoices in EN 16931 format are accepted across all EU member states, enabling smooth, interoperable trade and reducing the risk of rejections or delays due to incompatible formats.
• Higher Efficiency & Lower Costs: Automation eliminates manual data entry, reduces errors, and cuts costs related to printing, postage, and administrative labor.
• Improved Accuracy & Fewer Errors: Structured, validated data minimizes mistakes, leading to fewer disputes and less time spent on corrections.
• Interoperability & Business Agility: One standard enables easy connection with new partners and systems, supporting business growth and digital transformation.
• Faster Payments & Better Cash Flow: Automated, error-free processes speed up invoice approvals and payments, improving cash flow and financial visibility.
• Regulatory Compliance: Ensures adherence to EU and national laws, especially for public sector contracts, and helps avoid penalties for non-compliance.
• Enhanced Business Credibility: Reliable, standardized invoicing builds trust with partners and signals modern, compliant business practices.
• Supports Digital Transformation: Facilitates integration with ERP/accounting systems and prepares businesses for future digital and regulatory requirements.

EN 16931 Compared to Other E-Invoicing Standards (Global Perspective)

EN 16931 is a key standard in Europe, but e-invoicing is a global trend and there are other standards and frameworks out there. Below is a simple comparison between EN 16931 and some major e-invoicing standards or models worldwide, to put things in perspective:

Belgium’s E-Invoicing Mandate 

Belgium implemented the EU Directive 2014/55/EU, requiring public authorities to accept e-invoices in the EN 16931 format since 2019. This ensures all invoices sent to Belgian government entities must comply with the European standard.

Here’s an overview of Belgium’s e-invoicing mandate and how EN 16931 fits in:

• Mandatory B2G E-Invoicing: Belgium extended the requirement to suppliers, mandating that all business-to-government (B2G) invoices be electronic and EN 16931-compliant. The rollout was phased by region and contract size, with Flanders, Brussels, and Wallonia implementing requirements at different times. Simple PDFs are no longer accepted for these transactions.
• Platform-Agnostic, Peppol-Based System: Belgium chose a platform-agnostic approach, using the Peppol network for e-invoice exchange. The Mercurius platform acts as a national hub, routing EN 16931 invoices via Peppol to the correct public entity and providing tracking and accessibility for all business sizes.
• Upcoming B2B E-Invoicing Mandate: From January 1, 2026, Belgium will require all domestic B2B transactions between VAT-registered businesses to use structured e-invoices in the EN 16931 format, typically exchanged via Peppol. PDF invoices will no longer be VAT-compliant for B2B transactions. Some exemptions apply (e.g., simplified tax regimes, certain VAT-exempt activities).
• Scope and Exclusions:
• Technical and Practical Impact:

Conclusion

The EN 16931 Electronic Invoicing Standard plays a foundational role in Europe's drive toward seamless, efficient, and interoperable digital invoicing. By defining a common data model for e-invoices, EN 16931 ensures that invoices can be exchanged and understood across different systems and countries without manual intervention. In Belgium, this standard underpins both public sector (B2G) e-invoicing requirements and the country’s upcoming B2B e-invoicing mandate, making it essential for businesses to align with EN 16931 to remain compliant, competitive, and digitally agile. The standard’s structured format, focus on automation, and compatibility with delivery networks like Peppol help companies streamline their billing processes, reduce errors, lower costs, and speed up payment cycles.

As Belgium advances its digital agenda, EN 16931 compliance is becoming not just a regulatory necessity but a strategic advantage. Businesses that adopt this standard benefit from easier cross-border trade, enhanced operational efficiency, and better integration with public and private partners.