Insurers will sell you car insurance before you have a title. Most companies will start a policy without the title if you can prove ownership with a bill of sale, lease agreement or bank statement showing your vehicle loan.
Depending on where you live and how you bought the car, you may need proof of insurance before the title transfer.
Having insurance ready before the title transfer is a good idea. This ensures you're covered right away, especially if you plan to drive the car immediately after buying it.