If they demand payment from you, you can elect to pay, refuse to pay, or try to settle (work out an amount that you both are comfortable with). If you can't work out a mutually agreeable settlement or refuse to pay, the other driver can file a lawsuit against you for any costs, injuries, damages, etc. he claims to have suffered. You will have to defend against the lawsuit or else lose by default (like forfeiting a ball game). To win money from you, he will have to prove in court by a preponderance of the evidence (that it is more likel than not) that you were at fault in causing the accident (only an at fault driver has to pay) and the extent of his losses. You can defend by trying to show with your own evidence or testimony that you were not at fault, or that he was at fault, or that his injuries or costs are not as severe as he claims.If he wins--convinces the court that you were at fault--he will get a judgment against you for whatever amount he convinced the court of. If you do not pay, he can take collections efforts against you (such as garnishing your wages, levying on your bank account, executing on personal property, and/or putting a lien on real estate). Having an unpaid judgment against you will damage your credit.If you have insurance, your insurer should defend you and pay any judgment against you, at least up to the policy limits (an insurer is only responsible up to the policy limits). You should notify your insurer of any claims as soon as they are made. Most likely, after having a claim against you, your insurance cost will go up in the future.