ISO forms and why most commercial policies look alike

ISO forms are standard insurance policy forms written by the Insurance Services Office, now part of Verisk, and made available to insurers as an advisory organization. Most commercial general liability, property, auto and crime policies in the United States use ISO wording or a close copy, which is why a policy from one carrier reads like a policy from another. The wording is standard. The price, the endorsements and the underwriting are not.

Where standard forms came from

Standard wording is older than ISO. The NAIC's Product Filing Review Handbook (2024) notes that insurers in the mid-1800s wrote their own fire contracts and the lack of standard wording made coverage hard to interpret. Massachusetts adopted a standard fire form in 1873, New York adopted one in 1887, and by 1943 New York's "165-line" standard fire policy had been approved by reference in most states. Rating bureaus, a type of advisory organization, later developed to give insurers common statistics and form language. Today, the Handbook says, advisory organizations offer actuarial, statistical, underwriting and standard policy language services.

How ISO fits into the regulatory system

ISO is one of several advisory organizations, alongside AAIS, NCCI and the Surety and Fidelity Association of America. The NAIC handbook says these organizations are authorized to make filings for or on behalf of insurers, and that they develop loss costs, policy forms, risk classifications and rating rules that member insurers may use.

Three details explain how a standard form becomes your policy.

1. Use is voluntary. An insurer chooses to adopt an ISO form, either by filing it or by referencing ISO's filing with the state. It can also write its own form, or use ISO's with changes.
2. ISO provides loss costs, not final prices. After a late-1980s working group of NAIC regulators concluded that advisory organizations should not publish final rates, ISO and NCCI began filing only "advisory prospective loss costs." The insurer applies a loss cost multiplier to cover its own expenses and profit, and can adopt the loss costs unchanged or deviate from them with an explanation.
3. States regulate forms differently. Some require approval before a form is used, others only a filing. That is why ISO publishes state-specific amendatory endorsements, and why identical policy numbers can read slightly differently in different states.

That is also why two carriers can quote the same ISO general liability form at different prices. A hypothetical makes the point. Say the ISO loss cost for your class is $1.20 per $1,000 of sales and one carrier's multiplier is 1.50 while another's is 1.80. The rates are $1.80 and $2.16 per $1,000. On $2 million of sales, that is $3,600 against $4,320 before any credits, debits or other rating factors. The figures are invented; the mechanism is how most ISO-based pricing works (how commercial insurance premiums are calculated).

Reading a form number

An ISO form number tells you the line, the kind of form and the edition.

So CG 00 01 04 13 is the April 2013 edition of the occurrence form. Common prefixes you will meet:

Workers' compensation is different. Its standard policy, NCCI's WC 00 00 00, is written by NCCI, not ISO. Edition dates matter because ISO revises forms every few years. A form with an older edition date is not wrong, it is just older, and the later edition may contain changes that cut or expand coverage. See basic, broad and special causes of loss forms: what each covers for how the property causes-of-loss options differ.

Why the sameness is useful

• Case law. Courts have interpreted CG 00 01 phrases such as "occurrence," "insured contract" and "your work" for decades. A familiar form is more predictable in a dispute.
• Contracts and certificates. Leases and construction contracts often cite forms by number. A county's sample insurance requirements, for instance, call for CG 00 01 and accept additional insured endorsements CG 20 26 or CG 20 12 "or equivalents," according to a public Sonoma County template. See how to review the insurance requirements in a contract and additional insured endorsements explained. The contract insurance requirements checker helps compare a contract's demands with your policy.
• Comparison shopping. With the same base form, you can compare limits, deductibles and endorsements instead of deciphering different wording.

Where policies depart from ISO

Standard forms are a starting point. Several things change them.

• Endorsements. Every ISO coverage form can be altered with endorsements, including carrier-specific ones. Most coverage disputes turn on an endorsement. the endorsements small businesses most often need lists the usual ones.
• Proprietary forms. Large carriers often write their own general liability, package or businessowners forms that look like ISO but differ in places, such as how they define covered property or limit defense costs.
• Lines with no standard form. Cyber, D&O, Employment practices liability insurance (EPLI): what it covers and most professional liability policies are carrier-written. There is no ISO form for cyber coverage, for example. See cyber insurance: what it covers for a business.
• Surplus lines. Non-admitted insurers are not bound to filed forms and often use manuscript wording (excess and surplus lines insurance explained).
• Other advisory organizations. AAIS, a not-for-profit advisory organization that began in 1936 as the Mutual Marine Conference, offers its own forms to member carriers. A policy on AAIS wording is not ISO wording, even if it looks similar.
• Exclusions added to the standard. Verisk ISO issued generative AI exclusion endorsements CG 40 47, CG 40 48 and CG 35 08 in January 2026, according to Insurance Business (September 16, 2026). Insurers choose whether to use them.

Revisions and what they change

Every few years ISO files revised multistate forms. For general liability, ISO circular LI-GL-2026-208 (July 14, 2026) announced a revised CGL multistate forms package for policies written on or after October 1, 2026 in 48 jurisdictions, as reported by PropertyCasualty360. Each insurer and each state decides when to adopt a new edition, so your policy may carry an edition from 2013, 2019 or 2026. Treat a new edition date on your renewal as a prompt: ask your broker for a summary of what changed, then compare the forms. how to read a commercial policy: declarations, forms and endorsements shows how.

What to ask your broker

1. Is this the ISO form or the carrier's own wording, and which edition?
2. Which endorsements are carrier-specific, and what do they change?
3. How does this edition differ from last year's?
4. Does the contract language "or equivalent" match what this policy provides?
5. Are there state amendatory endorsements that change cancellation, notice or suit deadlines?

Key takeaways

• ISO is an advisory organization that offers standard forms, rules and loss costs; insurers choose whether to adopt them and set their own prices.
• A form number gives the line, the form and the edition date, so CG 00 01 04 13 is the April 2013 occurrence general liability form.
• Standard wording gives predictability, but endorsements, state amendments, proprietary forms and newer editions change what you actually own.
• Cyber, D&O and most professional liability policies have no standard ISO form, so the carrier's wording is the policy.