Unjust enrichment is a restitution-based theory. It does not depend on a contract or on a tort; it rests on the principle that a person who receives a benefit under circumstances making it unjust to keep it without paying must return the value of that benefit. The remedy is restitution -- restoring the gain -- rather than compensating for a loss.

The doctrine fills gaps where no enforceable contract governs but one party has nonetheless been enriched at another's expense. Courts sometimes describe the resulting obligation as a quasi-contract or a contract implied in law: an obligation the law imposes to prevent unfairness, not one the parties actually agreed to.

A common formulation requires: (1) the plaintiff conferred a benefit on the defendant; (2) the defendant knew of or appreciated the benefit; and (3) the defendant accepted or retained the benefit under circumstances that make retention without payment inequitable. Some jurisdictions phrase it as enrichment of the defendant, a corresponding deprivation of the plaintiff, and the absence of a legal justification for the enrichment.

The 'unjust' element is the heart of the claim. A benefit conferred officiously as a volunteer, or one the recipient had every right to keep, is not unjust enrichment.

Unjust enrichment commonly arises from mistaken payments, benefits conferred under a contract that turns out to be void or unenforceable, services rendered in the expectation of payment that never materialized, or a defendant who profits from the plaintiff's property or efforts without authorization.

A crucial limit: where a valid, enforceable contract governs the same subject matter, courts generally will not allow an unjust-enrichment claim to override the parties' agreed allocation of risk. The equitable remedy is for gaps the contract does not fill.

Plaintiffs prove the benefit conferred and its value, the defendant's awareness, and the inequity of retention -- often through invoices, transfers, records of services, or evidence of the defendant's resulting gain. The measure of recovery is typically the value of the benefit to the defendant, not the plaintiff's cost.

Defendants argue there was no cognizable benefit, that the plaintiff acted as a mere volunteer, that retention is not inequitable, or -- most powerfully -- that an express contract already governs the subject, foreclosing the equitable claim. Change of position or a valid justification for keeping the benefit are also defenses.

Unjust enrichment is frequently pleaded alongside breach of contract as a fallback: if the contract is found void, unenforceable, or nonexistent, the restitution theory can still capture the value transferred. It also anchors quasi-contract recoveries where the parties never reached agreement.

As a claim path, its elements and the contract-bar defense become decision nodes, and the restitutionary measure of recovery is a distinct value branch. In Juricratic you can war-game whether the contract or the restitution branch controls by dialing the enforceability of any governing agreement and the inequity of retention, then compare modeled recoveries. The dials are hypothetical inputs, not predictions.