A key milestone under the EU Green Bond Regulation ((EU) 2023/2631) (the Regulation) will be reached on 21 June 2026, when the transitional regime for external reviewers ends and the full supervisory framework becomes operational.

The Regulation, which has applied from 21 December 2024, established a voluntary “European Green Bond” (EuGB) label. Issuers opting to use the label must demonstrate that the proceeds of the bond are allocated in alignment with the EU Taxonomy, subject to flexibility provisions. A central feature of the regime is the requirement for an independent external reviewer to assess and confirm compliance with the Regulation’s requirements, both at issuance (via a pre-issuance review) and on an ongoing basis (via a post-allocation review).

Transitional period

During the initial 18‑month transitional period (which commenced on 21 December 2024), external reviewers have been permitted to operate on the basis of notification to ESMA, with “best efforts” compliance with the substantive requirements while the ESMA registration and supervision framework was developed.

To support the new external review regime under the Regulation, the Commission has adopted secondary legislation, including the following:

1. an Implementing Regulation (EU) 2025/2179 (in force), setting out the standard forms, templates, and procedures for applications by external reviewers seeking registration with ESMA.
2. an Implementing Regulation (EU) 2026/543 (published in the OJ on 17 June), setting out the standard forms and procedures for how external reviewers notify material changes to their registration information. This was published in the Official Journal of the European Union on 17 June 2026 and will enter force on the twentieth day following publication being 7 July 2026.
3. a Delegated Regulation on registration conditions (EU) 2025/2180 (in force), defining the conditions for registration, the criteria to assess the sound and prudent management of external reviewers, the appropriateness of the knowledge, experience and training of the external reviewers’ employees and the conditions under which external review activities may be outsourced.
4. a Delegated Regulation on systems and procedures (EU) 2026/544 (published in the OJ on 17 June), specifying the criteria for assessing the appropriateness, adequacy and effectiveness of the systems, resources and procedures of external reviewers, their compliance function, internal policies and procedures, assessment methodologies and information used for reviews, as well as the information and the form and content of applications for recognition of third-country external reviewers. This regulation was published in the Official Journal of the European Union on 17 June 2026 and will enter force on the twentieth day following publication being 7 July 2026.

Position from 21 June 2026

From 21 June 2026, the regime shifts materially:

• Mandatory ESMA registration: All entities providing external review services in respect of EuGBs must be formally registered with, and supervised by, ESMA. The transitional regime falls away and unregistered entities will no longer be permitted to provide external review services under the Regulation.
• Full regulatory compliance: External reviewers must comply in full with the organisational, governance and conduct requirements set out in the Regulation (as supplemented by RTS/ITS). The “best efforts” approach applicable during the transitional period ceases to apply.
• Ongoing ESMA supervision: Registered external reviewers will be subject to ongoing supervisory oversight by ESMA. This framework is designed to ensure the independence and quality of external reviews and to protect investor confidence.
• Third-country equivalence framework: The provisions governing non‑EU external reviewers (including equivalence, recognition and endorsement mechanisms) become operative, enabling access to the EU market subject to regulatory conditions.

Practical implications

This milestone represents a significant step in the operationalisation of the EU’s sustainable finance framework:

• For issuers, appointment of an ESMA‑registered reviewer becomes a strict requirement when using the EuGB label. Issuers should confirm the registration status of their chosen reviewer ahead of 21 June 2026.
• For external reviewers, the regime introduces a fully harmonised EU supervisory framework, with higher regulatory standards and governance requirements before entry.
• For investors and the market more broadly, the shift is intended to enhance credibility, comparability and investor confidence in green bonds, reinforcing the EuGB label as a “gold standard” in sustainable finance.

Takeaway

The 21 June 2026 deadline marks the transition from a soft‑launch phase to a fully regulated external review system, with mandatory ESMA registration, ongoing supervision and third‑country access frameworks in place. Entities currently providing, or intending to provide, external review services for EU Green Bonds should ensure they have obtained the necessary registration with ESMA ahead of 21 June 2026.

To discuss any aspect of the Regulation in more detail, please get in touch with your usual contact in our Debt Capital Markets Group.