Mahr (alternatively transliterated as mahr, mahar, mehr, or mehrieh) is a mandatory gift that the groom gives to his bride at the time of Islamic marriage. It is a contract that some Muslims enter into upon marriage, and it refers not to the contract of marriage itself, but to a contractual dowry to be paid by the husband to his wife in the event of divorce or death. In Islamic law, Mahr is a gift or contribution made by the husband-to-be to his wife-to-be, for her exclusive property, as a mark of respect for the bride, and as recognition of her independence. It is not, however, a gift in the traditional sense, but is in fact obligatory and the wife-to-be receives it as a right. Mahr can be cash, or any type of property given up front before the marriage or split into advance and deferred payments. The amount and timelines for payment will depend on customary considerations under Islamic law. In the case of deferred payment, the portion deferred has the effect of helping to look after a wife after divorce or after her husband’s death. Although a wife can waive payment of the Mahr, she is entitled to it as a matter of Islamic religious principle.

Mahr is distinct from dower in two ways: 1) Mahr is legally required for all Islamic marriages while dower is optional, and 2) Mahr is required to be specified at the time of marriage (when a certain amount is promised, if not paid immediately), while dower is not paid until the death of the husband. Mahr is also classified as a form of "bridewealth", described by anthropologists as payments made from the kin of the groom to the kin of the bride; however, Mahr is paid directly to the bride and not her parents.

Mahr is an obligation according to the Holy Quran, and it is the main aspect of Nikah. The gift of marriage (Mahr) is a sacred command. Although Islamic law recognizes Mahr without a written agreement, to enforce a Mahr under provincial legislation it must be in writing, signed by both parties and witnessed.