A public marriage license is mainly a document from the church or a state agency that gives a couple permission to marry. In article 16 of the Universal Declaration of Human Rights, it declares that "Men and women of full age, without any limitation due to race, nationality or religion, have the right to marry and to found a family. They are entitled to equal rights as to marriage, during marriage and at its dissolution. Marriage shall be entered into only with the free and full consent of the intending spouses."
Basically most of the couple would not be denied the permission to marry unless they fail to meet all the necessary requirements. In some cases, however, there are states that don’t allow marriage between people of the same sex which means that the couple would not be granted the said license.
The marriage license is rather a formality that can be used by the state in various legalities. It can also determine the rights and privileges of each spouse.
The procedure for obtaining a license conforms to the location of the couple. Marriage licenses have been issued since the Middle Ages. It is to permit a marriage which would otherwise be illegal.
Today, marriage licenses are legal requirements in some jurisdictions. If witnessed and signed by the couple, it would also serve as a record of the marriage itself.
In some jurisdictions, a pardon may be obtained if married without a license. Common-law-marriages and marriage by cohabitation and representation are recognized as well but these do not require a marriage license. On the other hand, in other jurisdictions the license is not even required at all.