How to hire a contractor you can trust on Long Island.

Nassau County and Suffolk County both require home improvement contractors to be licensed. Nassau County puts it plainly: it is against the law to operate a home improvement business in the county without a license.

Ask for the license number, then check it with the county before you sign. In Nassau, call the Office of Consumer Affairs at 516-571-2600, which can also tell you the firm's complaint history. In Suffolk, call Consumer Affairs at 631-853-4600 or use the county's online license search. Nassau's checklist also says the license number belongs in the contract.

New York's General Business Law says a home improvement contract, and every amendment to it, must be in writing and signed by all the parties. The Attorney General's office puts it the same way: state law requires a contractor to provide a written contract for home improvement work.

Among other things, the contract has to give the contractor's name, address, phone number, and license number, the approximate dates the work will begin and be substantially completed, a description of the work and the materials, and the agreed price. If you pay in stages, it has to list each payment. It must also tell you that you can cancel until midnight of the third business day after you sign.

Changes happen on almost every remodel: a different tile, a moved outlet, something found behind a wall. The law's writing rule covers amendments to the contract, the Attorney General's office says any verbal change must be added to the written contract, and Nassau County's checklist says all changes should be in writing.

Nassau's checklist also says to agree on a price for any changes or extra work not specified in the original contract, and to have both parties initial the changes. Settle it before the work is done, not after.

Ask who runs the job, who will be at the house each day, and who the subcontractors are. A common worry about contractors is that once the work starts, nobody is there watching it.

The Attorney General's office says to get references from the contractor and speak directly to former customers. Look at photos of the contractor's own jobs, and not only finished rooms: work in progress shows how a job is built. Ask what the job was and when it was done.

On Long Island, building permits come from the town, the city, or the village that has the house, and an incorporated village has its own building department. In the Town of Huntington, for example, the Building and Housing Division reviews building and site plans, issues building permits, and inspects construction as it progresses.

The Attorney General's office says to check with your local building department before beginning a project. Nassau County's checklist adds that, as the owner, you are responsible for either getting the permits or seeing that the contractor gets them. Ask your contractor which permits the job needs, who will apply for them, and who will meet the inspector.

Any one of these is a reason to slow down, ask more questions, or walk away.