1. Core Legal Answer & Context: 'Quasi-contracts,' also known as 'constructive contracts' or 'contracts implied in law,' are not contracts in the traditional sense because they do not arise from an agreement or mutual consent of the parties. Instead, they are obligations imposed by law to prevent unjust enrichment of one party at the expense of another. The Indian Contract Act, 1872, does not use the term 'quasi-contract' explicitly but deals with such obligations under the heading 'Of Certain Relations Resembling Those Created by Contract.' The underlying principle is equity, justice, and good conscience, ensuring that no one benefits unfairly from another's loss or effort.

These obligations are based on the legal fiction that a contract exists, even though there is no offer, acceptance, or consideration. The law creates these obligations to restore the status quo or provide compensation where it would be unconscionable for one party to retain a benefit received from another without payment.

2. Relevant Statutes and Sections:

• Indian Contract Act, 1872:
  • Sections 68-72: These sections deal with various types of quasi-contractual obligations:
    • Section 68 (Claim for necessaries supplied to person incapable of contracting, or on his account): If a person incapable of entering into a contract (e.g., a minor or a person of unsound mind) or anyone whom he is legally bound to support, is supplied by another person with necessaries suited to his condition in life, the person who has furnished such supplies is entitled to be reimbursed from the property of such incapable person.
    • Section 69 (Payment by interested person): A person who is interested in the payment of money which another is bound by law to pay, and who therefore pays it, is entitled to be reimbursed by the other.
    • Section 70 (Obligation of person enjoying benefit of non-gratuitous act): Where a person lawfully does anything for another person, or delivers anything to him, not intending to do so gratuitously, and such other person enjoys the benefit thereof, the latter is bound to make compensation to the former in respect of, or to restore, the thing so done or delivered.
    • Section 71 (Responsibility of finder of goods): A person who finds goods belonging to another, and takes them into his custody, is subject to the same responsibility as a bailee.
    • Section 72 (Liability of person to whom money is paid, or thing delivered, by mistake or under coercion): A person to whom money has been paid, or anything delivered, by mistake or under coercion, must repay or return it.

3. Important Landmark Cases:

• Moses v. Macferlan (1760): This seminal English case, decided by Lord Mansfield, is often cited as the origin of quasi-contractual principles. Lord Mansfield stated that 'the gist of this kind of action is that the defendant, upon the circumstances of the case, is obliged by the ties of natural justice and equity to refund the money.' This case laid the foundation for the principle of unjust enrichment.
• Fibrosa Spolka Akcyjna v. Fairbairn Lawson Combe Barbour Ltd. (1943 AC): This English case, though primarily about frustration of contract, significantly developed the concept of unjust enrichment as the basis for recovery in quasi-contractual claims, particularly for money paid for a consideration that has totally failed.

4. Clear Conclusion: Quasi-contracts, as recognized under the Indian Contract Act, are legal obligations imposed by law, not by agreement, to prevent unjust enrichment. They are founded on principles of equity, justice, and good conscience, ensuring fairness in situations where a formal contract is absent but one party has received a benefit at another's expense. Sections 68-72 of the Act classify these obligations, providing remedies for situations ranging from supplying necessaries to recovering money paid by mistake, thereby filling gaps where traditional contract law might not provide a remedy.