For example, in California, you must title a vehicle in your name before you can sell it. If you do not, the buyer will not be able to register the vehicle in their name.
In other states, such as Texas, it's possible to sell a vehicle without titling it as long as you have the original Certificate of Title signed by the previous owner and a properly completed bill of sale.
It's important to check with your local DMV or Department of Motor Vehicles to find out the specific laws and requirements for selling a vehicle in your state.