According to the Halacha
1. The obligation to return
(a) Anyone who has received an asset, service, or other benefit (hereinafter – the beneficiary) that came to him from another person (hereinafter – the benefactor), not by legal right, is obligated to return the benefit, or its equivalent, to the benefactor. If returning the benefit in kind is impossible or unreasonable, he must pay its value.
(b) A person lacking legal competence is obligated to return the benefit if it exists in kind, and is exempt from any obligation to pay.
(c) It is the same whether the benefit came from the action of the beneficiary, the action of the benefactor, or in another way.
Civil Law
(a) A person who has received, without a legal right, property, a service, or any other benefit (hereinafter: the recipient) that has come to him from another person (hereinafter: the conferring party) shall be obliged to restore the enrichment to the conferring party; and where restitution in kind is impossible or unreasonable, to pay him its value.
(b) It shall be immaterial whether the enrichment resulted from an act of the recipient, an act of the conferring party, or occurred in any other manner.
2. Exemption from return
(a) In a benefit that was not associated with a deficiency of the benefactor, the beneficiary is exempt from the obligation to return.
(b) Even where there is no deficiency to the benefactor, if the benefactor protested against the beneficiary or if the beneficiary discovered that the provider intended the benefit, he is obligated to return.
(c) An asset that is not in the possession of the beneficiary at the time of the claim, or he no longer benefits from the enjoyment he received, and he cannot reasonably be held responsible for its loss, he will be exempt from returning it.
Civil Law
The court may exempt the recipient, in whole or in part, from the duty of restitution under section 1, if it finds that the enrichment was not accompanied by a corresponding deprivation of the conferring party, or that other circumstances render restitution unjust
3. Deduction of expenses
The beneficiary is entitled to deduct from what he has to return any expenses that he has reasonably incurred, undertaken or invested to obtain the benefit. Where the beneficiary’s contribution to the creation of profits was substantial, he shall be entitled to a proportionate share in such profits.
Civil Law
The recipient may deduct from the amount to be restored any expenditure reasonably incurred, or any obligation reasonably undertaken, or any investment reasonably made, for the purpose of obtaining the enrichment.
4. Payment of Another’s Debt
Anyone who has paid another person's debt without being obligated to do so towards him is not entitled to return the debt payment, unless there was a reasonable reason for his intervention. Even in this case he is not entitled to this return except for what he gave for the debt payment.
Civil Law
A person who has discharged the debt of another without being obliged to do so vis-à-vis him shall not be entitled to restitution, unless the recipient had no reasonable ground to object to the discharge of the debt, in whole or in part; and such restitution shall not exceed the amount paid in discharge of the debt.
5. Acting to preserving Another’s Interests
(a) The fulfiller of his obligation and who performed a reasonable action to preserve the life, bodily integrity, health, family defect, or property of another person, and spent or committed to spend expenses in connection with this, the beneficiary is obligated to reimburse him for his reasonable expenses, including his obligations towards a third party; and if expected property damages were caused to the benefactor as a result of the action, he is entitled to compensation from the beneficiary, unless the beneficiary was present in the place and the benefactor did not stipulate that he would pay his damage, then he only has his due wage.
(b) For the purposes of the obligation to compensate under subsection (a), one whose assets served for the protection of such values shall be regarded as having acted to preserve them.
(c) A person who performed an action to save his property, if he intended by that action to also save the property of another person, the beneficiary must participate with him in the expenses, even if the rescuer was not required to increase the expenses for him.
(d) All that is stated in subsection (a):
When the rescuer's action was effective;
But when his action was not effective, he only has his wage, even if he stipulated with the beneficiary.
When the beneficiary initiated the use of the rescuer's property as stated in subsection (b), the rescuer is entitled to compensation for his damages even if the use of them was not effective.
(e) There is no obligation to reimburse or compensate under this section on a beneficiary who objected to the action or the use of assets or the amount of expenses or who had a reasonable reason to object to them, unless the action or the use of assets were for the preservation of his life, bodily integrity, or health.
Civil Law
(a) A person who, in good faith and in a reasonable manner, has taken action to protect the life, bodily integrity, health, dignity, or property of another person, without being obliged to do so vis-à-vis him, and who has incurred or undertaken expenses in connection therewith, shall be entitled to indemnification from the recipient for his reasonable expenses, including obligations toward third parties; and where, as a result of such action, property damage has been caused to the conferring party, the court may order the recipient to pay compensation to the conferring party, if it deems it just to do so in the circumstances of the case.
(b) For the purpose of liability to pay compensation under subsection (a), a person whose property was used for the protection of the aforesaid interests shall be deemed to be a person who has taken action to protect them.
(c) No duty of indemnification or compensation under this section shall apply where the recipient objected to the action, the use of property, or the amount of the expenses, or had reasonable grounds to object thereto, unless the action or the use of property was necessary for the protection of his life, bodily integrity, or health.
6. Application and Preservation of Remedies
The provisions of this law shall apply when there is no other agreement between the parties
Civil Law
(a) The provisions of this Law shall apply where no special provisions governing the matter are prescribed by any other law and where there is no other agreement between the parties.
(b) This Law shall also apply to the State.
(c) Nothing in this Law shall derogate from any other remedies.