A driver backs into your parked car in a grocery lot, apologizes, and then admits there is no policy behind the apology. The repair bill does not disappear because the other person cannot pay. This is the situation one short line on your own declarations page is built for, and it is worth understanding before you are standing in that lot with a phone in your hand.
Two different promises in one line
Uninsured and underinsured motorist coverage are usually sold together, but they answer two different problems. The first responds when the at-fault driver has no insurance at all, or cannot be identified after a hit-and-run. The second responds when that driver has insurance, but the limit is too small to cover the loss. In a serious injury claim, the second situation is often the more expensive one, because a minimum policy can be exhausted quickly.
Bodily injury coverage under this line can pay for medical bills, lost wages, and in some cases pain and suffering, up to the limit you chose. Property damage coverage, where it is offered, addresses the car itself. Which of these appear on your policy depends on the state and on what you selected, so read the actual line rather than assuming the label covers everything.
How it meets a collision deductible
Here is the part that surprises people. If you carry collision, your own carrier may repair the car regardless of who caused the crash, then pursue the other driver for reimbursement. That route usually involves your deductible. Uninsured motorist property damage coverage can in some states handle the same repair with a smaller deductible or none at all. Which path is better depends on the numbers on your policy, not on a general rule.
Ask the adjuster to walk through both options before authorizing the repair. It is a five-minute question that can change what you pay out of pocket, and it is much easier to ask before the shop has the car apart than after.
Where state rules change the answer
Some states require this coverage on every policy, some require it to be offered and allow a written rejection, and some treat the property damage portion differently from the injury portion. A few allow stacking, where limits from more than one vehicle on the same policy can be combined. These are state-level rules, not carrier preferences, which is why advice copied from a forum in another state can be actively wrong for you.
The practical move is to ask for a plain-language summary of how the coverage works where you live, and to keep it with the policy. When something happens, you will not be in a mood to decode statute references.
Questions worth asking before you sign
Is the limit per person or per accident? Does the underinsured portion apply when the other driver's limit is merely lower than yours, or only when it is exhausted? Is there a deductible on the property damage side? Does the coverage follow you as a passenger or pedestrian, or only while you are in the listed car? Four short questions, each with an answer that changes the value of what you are buying.
One risk is worth naming plainly: choosing the lowest available limit because it makes the premium look tidy. The difference between a minimum limit and one closer to your own liability limit is often modest in monthly terms, and it is the difference that matters most in the claim nobody plans for. Match this coverage to the level of protection you already bought for other people.