When parents live apart and one parent has custody of the kid, that parent may petition Family Court for an order requiring the "non-custodial parent" to pay child support. The other parent can either agree to the amount requested by the custodial parent or go to court and fight it. In New York, for example, the non-custodial parent can file what is called a paternity action. This action would be filed with the County Clerk's office where the custodial parent resides. If the non-custodial parent is able to prove he/she is the father of the child, then the court will issue an order requiring the custodial parent to provide his/her address so that payments can be sent directly to him/her. If the non-custodial parent does not know where the child lives, he/she can request a DNA test be done to establish paternity. The cost of this test is paid for by the government unless you can't afford it in which case there are programs available to help out. The purpose of filing the action is so that the non-custodial parent will receive notice if there is ever a change in the location of the child. He/she also will be given notice if the child gets married, has a baby brother or sister, etc.