How do I verify an arborist's certification?
Ask the arborist for their ISA certification number and full name, then look it up in the International Society of Arboriculture's public verification directory at treesaregood.org. Confirm the name matches the person who will actually assess your tree, not just the company. Check state licensing where it exists. If it does not check out, do not pay for their advice.
"ISA Certified" is printed on a lot of trucks, and most of the time it is true of at least one person at the company. Checking takes five minutes and costs nothing. It matters most when you are paying for advice or a report.
| Check | Where | What a pass looks like | What a fail means |
|---|---|---|---|
| ISA Certified Arborist credential | ISA public directory, treesaregood.org | Name and number match; status active | Do not rely on them for diagnosis or reports |
| The person, not the company | Ask directly | The certified person will be on site or will write the report | You are hiring a tree service, which may be fine |
| Specialty credentials (TRAQ, Board Certified Master Arborist, ASCA RCA) | Same ISA directory; ASCA's own directory for consulting arborists | Listed under the person's name | Ask for someone qualified if you need a formal risk assessment ($300–$1,000+) |
| State or city license | State contractor board or agriculture department | Company holds the license where one is required | Illegal to operate there; walk away |
| Insurance | Certificate sent from the insurer | General liability and workers' compensation, current, company name matches | Do not let them work on your property |
How do I verify an ISA certification, step by step?
- Ask for the name and certification number. Ask for the full name as it appears on the certification and the ISA certification number. A certified arborist expects the question and answers it without hesitation.
- Look it up in ISA's public directory. Go to the International Society of Arboriculture's consumer site, treesaregood.org, and use the credential verification or find-an-arborist search. Enter the name or number and confirm the listing shows an active ISA Certified Arborist credential.
- Match the person to the job. Confirm the listed person is the one who will assess your tree or supervise the work, not just the owner or the name on the truck. Ask: will you be the one on site?
- Check state or city licensing where it exists. Search your state contractor board or department of agriculture. Most states have no arborist license; where one exists, confirm the company holds it. Then ask for a certificate of insurance sent from the insurer.
- Decide what to do with the result. Everything matches: proceed. The number fails or belongs to someone who will not be involved: do not rely on that person for diagnosis or a report. Find and vet a different company, or treat this one as a cutting crew only.
How do I look up an ISA Certified Arborist?
ISA runs a consumer-facing site, treesaregood.org, with a public directory that lets anyone search certified arborists by name, certification number, or location. The listing shows the credentials the person holds and whether they are current. It is free, and it is also the tool to use to find an arborist if you do not have a name yet. Because certification lapses if the arborist does not earn 30 CEUs every 3 years, a listing that shows an active status is worth more than an old certificate on an office wall. Our own reviewers' numbers appear in the attribution block on every page and can be checked the same way. What the credential covers is on what is an ISA Certified Arborist?
What if the company is certified but the person isn't?
Then the company is telling the truth in a narrow way. ISA certifies individuals, not businesses, so "we are ISA Certified" means at least one employee holds the credential. The crew that shows up may hold nothing, which is normal and does not make them bad at cutting. The problem is only when the certified person is a name on the website and never sees your tree. If you are paying for a diagnosis, a risk rating, or a written report, the certified person needs to be the one who does it and signs it. How the two roles differ is on arborist vs. tree service.
Are arborists licensed by the state?
Mostly not. Arboriculture is unlicensed in most of the US, which is why the ISA credential carries so much weight. A few states license tree care companies or arborists, and some cities require a permit or registration for commercial tree work within their limits. Where a license exists, it is a legal requirement to operate and a separate check from ISA certification. Your state contractor licensing board or department of agriculture is the place to look. Whether or not your state licenses the work, insurance is the check that protects your house; see how to get proof of a tree service's insurance.
What should I do if the certification doesn't check out?
Ask once more, carefully. A nickname, a hyphenated surname, or a transposed digit can hide a real listing. If it still fails, the person is not currently ISA certified, whatever the truck says. Do not pay them for a diagnosis or a report, because the report will carry no weight with a neighbor, insurer, or city. You can still consider the company for straight removal work if the insurance checks out, but weigh the fact that they misrepresented a credential. The rest of the vetting process, from the written quote to references to red flags, is on how to vet a tree service.
Does certification mean they're insured?
No. ISA checks knowledge; it has no view into whether a person or company carries general liability or workers' compensation coverage. Ask for a certificate of insurance sent directly from the insurance agent to you, confirm the company name matches, and confirm both coverages are in force for the dates of the work.
No independently confirmed professional review is on file yet.
Not yet independently reviewed. General information, not legal advice. Licensing rules vary by state and city; check your local requirements.