The five most-cited ESG rating systems — MSCI, Morningstar Sustainalytics, ISS ESG, CDP, and EcoVadis — measure different things, on different scales, in different directions. MSCI grades industry-relative resilience on an AAA–CCC letter scale; Sustainalytics scores absolute unmanaged risk from 0 to 100 where lower is better; ISS ESG flags “Prime” status on an A+ to D- scale; CDP scores environmental disclosure from A to D-; and EcoVadis awards medals to suppliers by percentile rank. Because they define and weight “ESG” so differently, their scores for the same company correlate only about 0.54 on average. This guide explains each methodology, why the numbers disagree, and how to improve every one.
ESG ratings at a glance: the five systems compared
| Provider | Owned by | What it measures | Scale & direction | Relative or absolute | Primary audience |
|---|---|---|---|---|---|
| MSCI ESG Ratings | MSCI Inc. | Resilience to financially material, industry-specific ESG risks & opportunities | AAA → CCC (7 tiers); 0–10 underlying score. Higher is better. | Industry-relative (vs. GICS sub-industry peers) | Asset managers, index funds |
| Morningstar Sustainalytics | Morningstar | Magnitude of a company’s unmanaged ESG risk | 0–100 risk score; 5 bands (Negligible → Severe). Lower is better. | Absolute (comparable across industries) | Investors, brokerages, risk teams |
| ISS ESG Corporate Rating | ISS STOXX (Deutsche Börse) | Absolute ESG performance vs. demanding best-in-class expectations | A+ → D-; “Prime/Not Prime” threshold; decile rank 1–10. Higher is better. | Absolute grade + relative decile | European institutional investors |
| CDP | CDP (nonprofit) | Quality of environmental disclosure and action (climate, water, forests) | A/A- → D/D- (+ F for non-response). Higher is better. | Absolute (criteria-based) | Investors & procurement |
| EcoVadis | EcoVadis | Quality of a supplier’s sustainability management system | 0–100 score; Medals by percentile (Bronze → Platinum). Higher is better. | Relative (percentile vs. all assessed companies) | Procurement / supply-chain teams |
The single most important takeaway: a “good” score in one system does not translate to another, because the systems are not measuring the same construct. MSCI asks “is this company managing its material risks better than its peers?” Sustainalytics asks “how much unmanaged risk is left on the table, in absolute terms?” CDP asks “how good is this company’s environmental disclosure?” Comparing a Sustainalytics “Low Risk” to an MSCI “AA” is comparing different questions, not different answers to the same question.
Why ESG ratings disagree (the research most people miss)
Credit ratings from Moody’s and S&P correlate at roughly 0.99. ESG ratings do not come close. The landmark study on this is “Aggregate Confusion: The Divergence of ESG Ratings” by Berg, Kölbel & Rigobon, published in the Review of Finance (2022). Examining six major raters, they found:
- Average correlation of just 0.54 across ESG ratings, ranging from 0.38 to 0.71.
- Governance ratings are the least correlated, at 0.30 — the dimension investors often assume is most objective is actually where raters disagree most.
- The social dimension correlates at about 0.42.
They decompose the disagreement into three sources:
- Measurement (56%) — raters measure the same attribute (e.g., “employee turnover”) using different indicators and data, and reach different conclusions.
- Scope (38%) — raters include different sets of attributes. One counts lobbying; another doesn’t.
- Weight (6%) — raters weight the same attributes differently.
The study also identified a “rater effect” (a halo): once an agency forms an overall view of a company, that view bleeds into how it scores individual categories. The practical consequence — confirmed in follow-on research — is that ESG rating divergence sends companies mixed signals about which actions the market actually values, and can dampen the incentive to improve.
What this means for you: never treat a single ESG score as ground truth. Triangulate across providers, and always ask what the rating measures before you act on it.
MSCI ESG Ratings: industry-relative resilience (AAA–CCC)
What it measures. MSCI ESG Ratings assess a company’s resilience to financially material, industry-specific ESG risks and opportunities. It is explicitly a financial materiality lens — “which ESG issues could hit the bottom line in this industry, and how well is this company managing them?”
The scale. Companies receive a 0–10 underlying score that maps to a seven-tier letter rating:
- Leader: AAA, AA
- Average: A, BBB, BB
- Laggard: B, CCC
How it works. MSCI identifies the Key Issues that are material for each GICS sub-industry. Each Environmental or Social Key Issue carries a weight of roughly 5% to 30% of the total rating, set according to how much the industry contributes to that issue’s negative externality and how quickly the issue is expected to materialize. Scores are then normalized within each industry, so the rating is fundamentally peer-relative: an AA tells you the company leads its industry on managing material risks, not that it is “sustainable” in an absolute sense.
Worth knowing for 2026: MSCI announced a multi-stage ESG Ratings model update (disclosed October 2025) that is transitioning through 2026. If you are benchmarking or citing a specific rating, confirm it against MSCI’s current model rather than an older snapshot.
How to improve an MSCI rating: focus only on the Key Issues MSCI deems material for your sub-industry (managing an immaterial issue won’t move the score), strengthen disclosure on those issues, and remember the score is relative — improvement requires outpacing peers, not just improving in absolute terms.
Morningstar Sustainalytics: absolute unmanaged risk (0–100, lower is better)
What it measures. The Sustainalytics ESG Risk Rating measures the magnitude of a company’s unmanaged ESG risk — the portion of material ESG exposure that the company has not addressed through programs and policies. Crucially, it runs in the opposite direction from MSCI: a lower score is better.
The scale. Scores run 0 to 100 and sort into five risk categories:
- Negligible: 0–10
- Low: 10–20
- Medium: 20–30
- High: 30–40
- Severe: 40+
How it works. For each Material ESG Issue (MEI), Sustainalytics calculates Exposure (how much risk the business is inherently subject to) and then subtracts Managed Risk (the part addressed by the company) — plus a recognized band of risk that is simply unmanageable for that business. Unmanaged Risk = Exposure − Managed Risk. Because exposure is assessed at the sub-industry level but the final score is absolute, Sustainalytics ratings are designed to be comparable across industries and regions — a key difference from MSCI’s peer-relative approach. This is the rating you most often see surfaced on retail brokerages and finance portals.
How to improve a Sustainalytics score: close the gap between exposure and management — demonstrate concrete programs, policies, and outcomes on your highest-exposure MEIs. Because the score is absolute, real management improvements move it even if peers don’t change.
ISS ESG Corporate Rating: “Prime” status (A+ to D-)
What it measures. Now part of ISS STOXX (Deutsche Börse Group), the ISS ESG Corporate Rating evaluates a company against demanding, absolute best-in-class performance expectations for its industry.
The scale. A twelve-grade scale from A+ (best) to D- (worst), with two headline outputs:
- Prime / Not Prime: companies that clear an industry-specific threshold (often C+, but higher for industries with greater ESG exposure) earn “Prime” status — a signal of ESG investability.
- Decile rank (1–10): shows relative standing within the industry, where 1 is the strongest and 10 the weakest.
How it works. ISS ESG combines an absolute letter grade (against a fixed bar) with a relative decile rank (against peers), so you get both “did it meet the standard?” and “how does it rank?” in one rating. As of 2025, ISS defines SMEs as companies with fewer than 500 employees and under USD 500 million in revenue, reflecting expanding mandatory sustainability reporting.
How to improve an ISS ESG rating: identify the industry-specific Prime threshold and the absolute criteria behind it, then prioritize the indicators that lift you above the Prime line — the binary Prime status often matters more to investors than incremental grade movement.
CDP: environmental disclosure, scored A to D-
What it measures. CDP is different in kind from the others — it is a nonprofit disclosure platform, not a paid third-party rater. Companies respond to CDP’s questionnaire and are scored on the completeness and ambition of their environmental disclosure and action across Climate Change, Forests, and Water Security (with new scoring for cocoa, coffee, and rubber added in 2025).
The scale. Four bands, each reflecting a level of progress:
- A / A- — Leadership (the “A List”)
- B / B- — Management
- C / C- — Awareness
- D / D- — Disclosure
- F — failure to provide sufficient information / non-response
How it works. A company must satisfy CDP’s “Essential Criteria” at each level to progress — and as of 2025 those criteria apply at every tier, not just the top. A notable 2025 change: companies must have Scope 1 and Scope 2 emissions externally verified to reach the highest scores, and Forests and Water Security are now publicly scored for the financial-services sector. Because CDP rewards disclosure quality, a high CDP score signals transparency and process maturity — not necessarily low ESG risk.
How to improve a CDP score: map your response against the Essential Criteria for the level you’re targeting, secure third-party verification of Scope 1 & 2 emissions early, and treat the questionnaire as a year-round data project rather than an annual scramble.
EcoVadis: supply-chain medals by percentile
What it measures. EcoVadis assesses the quality of a company’s sustainability management system — primarily for procurement and supply-chain vetting. It is evidence-based: companies submit documentation, which EcoVadis evaluates through a Policies–Actions–Results (P-A-R) lens.
The scale. A 0–100 score across 21 criteria in four themes — Environment; Labor & Human Rights; Ethics; and Sustainable Procurement — translated into medals by percentile:
- Platinum: top 1% of assessed companies
- Gold: top 5%
- Silver: top 15%
- Bronze: top 35%
How it works. Medals are awarded relative to all companies assessed in the prior 12 months, so the bar moves with the population. A company is not eligible for any medal if its score in any single theme falls below 30, which prevents one strong theme from masking a weak one. As of January 2025, EcoVadis displays unrounded theme scores (e.g., 68/100) and uses them in the overall calculation.
How to improve an EcoVadis medal: close your weakest theme first (the sub-30 cutoff is the most common medal-blocker), and supply concrete evidence for Policies, Actions, and Results — claims without documentation don’t score.
How to use multiple ESG ratings together
Because each system answers a different question, the right move is to read them as complementary, not competing:
- Want financial-materiality and peer benchmarking? Lead with MSCI.
- Want an absolute, cross-industry risk number? Lead with Sustainalytics.
- Need a Prime/Not-Prime investability screen (especially in Europe)? Use ISS ESG.
- Assessing environmental transparency and climate action? Use CDP.
- Vetting a supplier? Use EcoVadis.
When two providers disagree sharply on the same company, that’s signal, not noise: it usually means they scope ESG differently (the 38% scope-divergence finding) or weight a controversy differently. Read the underlying sub-scores, not just the headline grade.
For a deeper walkthrough of how each scoring methodology is built and provider-specific tactics for lifting a score, see our companion guide to ESG ratings methodology and rating-improvement strategy.
Frequently asked questions
Which ESG rating is the most accurate?
None is definitively “most accurate” because they measure different things. MSCI and ISS ESG measure managed performance and resilience; Sustainalytics measures unmanaged risk; CDP measures environmental disclosure; EcoVadis measures supply-chain management systems. “Accuracy” depends on the question you’re asking. The more useful goal is to match the rating to your use case and triangulate across at least two.
Why does the same company get different ESG scores?
Because raters disagree on what to measure (scope), how to measure it (measurement), and how to weight it (weight). Research by Berg, Kölbel & Rigobon (2022) found ESG ratings correlate only about 0.54 on average, with measurement differences driving 56% of the divergence. A “rater effect” halo also nudges category scores toward each agency’s overall view of the company.
Is a low Sustainalytics score good or bad?
Good. The Sustainalytics ESG Risk Rating runs 0–100 where lower is better — a low score means little unmanaged risk. This is the opposite of MSCI, CDP, ISS ESG, and EcoVadis, where higher is better. Reversing this direction is one of the most common ESG-rating mistakes.
What does an MSCI rating of A or BBB mean?
On MSCI’s AAA–CCC scale, both A and BBB fall in the “Average” band — the company is neither a leader (AAA/AA) nor a laggard (B/CCC) at managing the ESG risks material to its industry. Because the rating is industry-relative, the same letter can reflect very different absolute practices across sectors.
Is CDP an ESG rating?
Not in the traditional sense. CDP is a nonprofit environmental disclosure platform that scores the quality of a company’s reporting and action on climate, water, and forests (A to D-). It rewards transparency and management maturity rather than scoring overall ESG risk, which is why CDP is best read alongside a true risk or performance rating.
Does MSCI use CDP data?
ESG raters draw on many overlapping public sources — corporate filings, CDP disclosures, regulatory data, news and NGO reports — but each applies its own model, indicators, and weights on top. Shared inputs do not produce shared conclusions, which is a core reason ratings still diverge even when raters read the same underlying disclosures.
What’s the difference between EcoVadis Gold and Platinum?
Both are percentile awards: Platinum goes to the top 1% of companies assessed by EcoVadis in the prior 12 months, and Gold to the top 5%. Because they’re relative to the assessed population, the score needed for each medal can shift year to year. No medal is awarded if any single theme scores below 30.
Sources & further reading
- MSCI, ESG Ratings Methodology (AAA–CCC scale, industry-relative Key Issues).
- Morningstar Sustainalytics, ESG Risk Ratings (0–100 unmanaged-risk scale, five risk categories).
- ISS ESG, Corporate Rating & Prime Status (A+ to D-, decile rank).
- CDP, How CDP Scores Companies (A to D- disclosure scoring on climate, water, forests).
- EcoVadis, Medals & Badges (percentile medals across four themes).
- Berg, Kölbel & Rigobon (2022), “Aggregate Confusion: The Divergence of ESG Ratings,” Review of Finance.