How Green Bonds Actually Work: The Four Components Every Issuer Must Meet

The global green bond market has grown from a niche instrument to a mainstream financing tool — but the standard behind it remains something most companies exploring green finance for the first time have never actually read. The Green Bond Principles (GBP), governed by the International Capital Market Association (ICMA), are voluntary process guidelines published alongside three sibling frameworks — the Social Bond Principles (SBP), Sustainability Bond Guidelines (SBG), and Sustainability-Linked Bond Principles (SLBP) — all under one shared governance structure with the stated mission of promoting the role that global debt capital markets can play in financing progress toward environmental and social sustainability.

"Voluntary" doesn't mean optional if you want your bond to be credible to institutional investors. The Principles exist specifically to underpin market integrity through transparency and disclosure — and increasingly, that credibility is verified by independent third parties before an issuance ever reaches the market.

What a Green Bond actually is, precisely

The GBP defines a Green Bond with specificity that matters: any type of bond instrument where the proceeds — or an equivalent amount — will be exclusively applied to finance or refinance, in part or in full, new and/or existing eligible Green Projects, aligned with the four core components of the Principles.

That word "exclusively" is doing a lot of work. A bond that finances general corporate purposes with vague sustainability language attached is not a green bond under this standard — regardless of what the marketing materials say.

The four core components, explained

1. Use of Proceeds — This is the foundation. The bond documentation must specifically designate which categories of Green Projects the proceeds will fund. The GBP provides high-level eligible categories, recognizing that understanding of environmental issues continues to evolve, while allowing issuers to reference more specific taxonomies (like the EU Taxonomy) for additional precision.

2. Project Evaluation and Selection — The issuer must clearly communicate the environmental sustainability objectives of the projects, the process for determining project eligibility, and any related eligibility criteria. This isn't a one-time disclosure — it needs to be a documented, repeatable process.

3. Management of Proceeds — Net proceeds should be tracked in a formal internal process, and the balance of unallocated proceeds should be regularly disclosed. Investors need to know not just what the money was supposed to fund, but that it actually went there.

4. Reporting — Issuers must keep readily available, updated information on the use of proceeds, renewed annually until full allocation, and promptly in case of material developments. Increasingly, this includes both qualitative performance indicators and, where feasible, quantitative performance metrics.

The 2025 update most companies miss: Green Enabling Projects

The 2025 edition of the GBP includes an important clarification that expands what qualifies: Green Enabling Projects. These are activities that aren't green in themselves, but are necessary components of an enabled Green Project's value chain — critical to its development, manufacturing, implementation, or scaling, even without generating direct environmental benefit on their own. These projects establish the necessary conditions for the success and existence of Green Projects. The 2025 edition also expanded the definition of Green Projects to explicitly include "activities" alongside assets, investments, and related expenditures — not just discrete capital projects.

This matters strategically: a company whose core product isn't inherently "green" may still have specific projects, investments, or activities within its value chain that qualify under this expanded framework — often overlooked because the company assumes green finance is only for renewable energy or similarly obvious categories.

What a real SQS1-rated framework looks like: the Iberdrola case

To understand what rigorous compliance with these four components looks like in practice, consider Iberdrola's Framework for Green Financing, which received an SQS1 ("Excellent") Sustainability Quality Score from Moody's in December 2023 — the highest rating on Moody's scale. Moody's assessment found that eight out of ten activities across two of five eligible categories adhere to EU Taxonomy criteria, and that the issuer meets 69 of 78 assessed technical screening criteria.

Iberdrola's framework organizes its use of proceeds into five specific eligible categories: smart grids, renewable energy, sustainable customer solutions, electric mobility, and green hydrogen — not a vague commitment to "sustainability," but discrete, auditable categories that map directly onto the GBP's Use of Proceeds requirement. The framework sits on top of over €140 billion invested in energy transition since 2000, with Science Based Targets initiative (SBTi)-verified targets for carbon neutrality in scopes 1 and 2 by 2030, and net-zero across all scopes — including scope 3 — before 2040.

This illustrates a principle worth internalizing: the framework document is only as credible as the operational history and verified targets that sit behind it. Moody's didn't evaluate Iberdrola's intentions — it evaluated 78 specific technical screening criteria against documented evidence.

Beyond bonds: the broader family of instruments

The Green Bond Principles don't stand alone. The 2025 edition explicitly notes that issuer-level sustainability commitments can be expressed as an alternative to — or supplement of — a pure use-of-proceeds focus, through Sustainability-Linked Bonds, as well as dedicated issuer strategies and disclosures recommended by the Climate Transition Finance Handbook for communicating Paris-aligned transition plans.

The key distinction worth understanding:

Green/Social/Sustainability Bonds are use-of-proceeds instruments — the money is tied to specific projects, evaluated, tracked, and reported against the four core components above.

Sustainability-Linked Bonds work differently — they're tied to the issuer's overall sustainability performance and targets, not specific project proceeds. This can be a better fit for companies whose sustainability story is about overall transformation rather than discrete, fundable projects.

What this means before you approach the market

Before any company begins conversations with underwriters about a green bond, three questions determine whether the process will be smooth or painful — questions the Iberdrola case answers concretely:

Can you specifically categorize what the proceeds will fund — not generally, but against defined eligible categories, the way Iberdrola names exactly five?
Do you have (or can you build) the internal tracking process that proceeds management requires, backed by an operational history like Iberdrola's two decades of documented transition investment?
Are you prepared for the ongoing annual reporting commitment against specific technical screening criteria — not a one-time disclosure at issuance, but a structure that can withstand the kind of 78-criteria assessment Moody's performed?

How Sustek.co prepares organizations for this process

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Sustainability Command — Maintain the reporting infrastructure this requires (Quarterly, from $1,500/month)

The reporting component of the GBP is not a one-time exercise — it requires continuous data infrastructure to track proceeds and report annually until full allocation, exactly the kind of ongoing verification that earns an SQS1 rating.

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Frequently asked questions

Are the Green Bond Principles legally mandatory? No — they're voluntary process guidelines. However, institutional investors increasingly expect alignment with them, often verified through independent Second Party Opinions like Moody's SQS rating system, as a baseline for considering a bond "credibly green" and accessing the best terms in the market.

What's the difference between a Green Bond and a Sustainability-Linked Bond? A Green Bond ties proceeds to specific, predefined project categories — evaluated and tracked against the four core components. A Sustainability-Linked Bond ties the bond's terms to the issuer's overall sustainability performance against targets — useful when a company's transformation story isn't reducible to discrete fundable projects.

What's a "Green Enabling Project" and why was it added in 2025? It's an activity that isn't green in itself but is a necessary component of an eligible Green Project's value chain — critical to its development, manufacturing, or scaling. The 2025 edition added this category to recognize that some essential supporting activities don't generate direct environmental benefit on their own but are still legitimate parts of a green financing strategy.

Does my company need to be in Europe to issue under these principles, or aligned to the EU Taxonomy? No — the Green Bond Principles are governed by ICMA, an international body, and are used by issuers globally. Alignment with the EU Taxonomy, as Iberdrola demonstrates, is optional additional detail that many non-European issuers include because global institutional investors increasingly use it as a comparison reference.

Sources: International Capital Market Association, "Green Bond Principles: Voluntary Process Guidelines for Issuing Green Bonds" (June 2025 edition); Moody's Investors Service, "Iberdrola S.A.: Second Party Opinion – Framework for Green Financing" (December 2023); Iberdrola, "Framework for Green Financing" (December 2023); Sustek.co Sustainability Transformation Tiers (sustek.co/services).