Do I have to have car insurance on my car?

Yes. It is illegal to drive without liability car insurance.  Driving a vehicle without insurance is a criminal offense and can result in fines, jail time, and suspension of your driver’s license.  Always carry proof that you have insurance in your vehicle.  Proof of insurance can be kept as a paper copy in your car or electronically on your phone.  The minimum requirement in Montana is $25,000 for personal injury and $20,000 for property damage.  

Can I get in trouble if I'm driving a friend's car and she doesn't have car insurance?

I'm an out of state student, do I need a Montana drivers' license?