Who can perform a marriage ceremony?
Usually the state laws provide any recognized member of the clergy (such as a Priest, Minister, Rabbi, Imam, Cantor, Ethical Culture Leader, etc.), or a judge, a court clerk, and justices of the peace have authority to perform a marriage. However in some states even the clergy must be first certified or licensed.
Some states have laws that permit other persons to apply for authority to perform marriage ceremonies. For example, California law permits anyone to apply for permission to become a Deputy Commissioner of Marriages -- the grant of authority is valid for one day -- and thus officiate at the wedding of family or friends on that one day.