## Introduction

This guide explains two different areas of US law that often come up in everyday disputes: unjust enrichment (a civil remedy focused on restitution) and criminal trespass (a property crime). Although they address different problems, both turn on clear elements and practical steps you can take to prevent issues or respond if they arise.

Unjust enrichment deals with situations where one person receives a benefit at someone else’s expense in circumstances the law treats as unfair. The remedy is restitution—returning money or the value of benefits.

Criminal trespass involves entering or remaining on property without permission after notice has been given. It is enforced by the state and can lead to fines or other penalties.

Note: State law varies. Always check your state statutes or speak with a qualified attorney for advice on a specific case.

## What You'll Learn

- What unjust enrichment means and the elements courts look for
- Common defenses to unjust enrichment and typical remedies (restitution, quantum meruit)
- What criminal trespass covers, including unauthorized entry, failure to leave, and posted property
- How courts treat trespass on clearly posted or fenced property
- Real-world criminal trespass case examples: People v. Johnson, State v. Smith, and Doe v. State
- Practical steps for property owners, businesses, and individuals to prevent disputes
- Where unjust enrichment fits alongside contract concepts like promissory estoppel and specific performance

## Core Concepts

### Unjust Enrichment (Civil Restitution)

Definition

- Unjust enrichment occurs when one person is enriched at another’s expense in circumstances the law regards as unfair. The court can impose an obligation to make restitution.

Common Elements

- Benefit conferred: The plaintiff provided money, services, or other value to the defendant.
- Knowledge or acceptance: The defendant knew about the benefit or accepted it.
- Unfair to keep without paying: It would be unfair to let the defendant retain the benefit without compensating the plaintiff.
- No adequate remedy at law: Often, there is no suitable contract claim or other legal remedy that covers the situation.

Typical Remedies

- Restitution of money paid by mistake or under invalid contracts
- Quantum meruit (reasonable value of services)
- Constructive trust or equitable lien in some cases involving property

Frequent Defenses

- Gift: The benefit was intended as a gift.
- Volunteer/officious intermeddler: The plaintiff imposed a benefit without request or justification.
- Contract covers the subject: An express contract (even with another party) may block a restitution claim.
- Change of position: The defendant reasonably relied on the benefit and cannot return it without hardship.
- Illegality: Courts will not order restitution in some unlawful arrangements.

Tip: Keep clear records—agreements, invoices, emails, and payment details often decide whether a benefit was requested and whether a restitution claim is appropriate.

### Criminal Trespass (Property Crime)

Definition

- Criminal trespass generally covers entering or remaining on property without permission after notice, or in a manner prohibited by statute (such as posted or fenced property).

Core Elements (state wording varies)

- Unauthorized entry or remaining: The person enters or stays on property without permission.
- Notice: The person had notice that entry or presence was not allowed. Notice can be given verbally by an owner or agent, or through posted signs, fencing, locked doors, or clearly restricted areas.
- Intent level: Many states require that the person knew or should have known entry was forbidden or that they were required to leave when told.

Common Types

- Unauthorized entry after hours into a building with posted restrictions
- Refusing to leave after being asked by the owner or authorized person
- Entering fenced or clearly posted “No Trespassing” property

Penalties and Defenses

- Penalties: Usually a misdemeanor; penalties can include fines, probation, community service, and in some cases, jail. Penalties can be higher for trespass in dwellings or sensitive locations.
- Defenses: Consent, necessity (e.g., emergencies), public rights-of-way or easements (where applicable), or lack of proper notice.

Practical Note

- Signage matters. Clear “No Trespassing” signs and physical barriers help prove notice. Many states have specific rules on sign placement and wording.

## Key Examples or Case Studies

Unjust Enrichment: Simple Scenario

- Scenario: A homeowner mistakenly pays a contractor twice for the same job due to a billing error. The contractor realizes the overpayment and keeps the money.
- Why it matters: The contractor received a benefit (extra payment) at the homeowner’s expense. A court could require restitution of the overpayment.

People v. Johnson — Unauthorized Entry

- Facts: The defendant entered a commercial building after business hours without permission. Signs on the doors clearly prohibited entry.
- Outcome: Charged with criminal trespass based on unauthorized entry and posted notice.
- Takeaway: After-hours entry into posted private property can meet the elements even if no other crime occurs.

State v. Smith — Failure to Leave

- Facts: The defendant remained on private property after the owner asked him to leave.
- Outcome: Convicted of criminal trespass based on refusal to depart.
- Takeaway: Once told to leave by an authorized person, remaining on the property can constitute trespass even without physical barriers or signs.

Doe v. State — Trespass on Posted Property

- Facts: The defendant entered a fenced area with “No Trespassing” signs at access points.
- Outcome: Charged with criminal trespass. Clear signage and fencing supported notice.
- Takeaway: Fencing and signs provide strong evidence that entry was prohibited.

## Practical Applications

For Potential Unjust Enrichment Claims

- Identify the benefit: Document the money paid, services performed, or property provided.
- Show acceptance: Keep emails, texts, invoices, or acknowledgments that the other party knew and accepted the benefit.
- Quantify the value: Keep receipts, market rates, or expert estimates for the reasonable value of services or benefits.
- Consider defenses: If the benefit was a gift or unsolicited, recovery may fail.
- Choose the forum: Smaller amounts may fit small claims court; larger disputes may require civil court.
- Demand first: A clear written demand for repayment or fair value often resolves the issue without litigation.

For Property Owners and Managers (Trespass Prevention)

- Post clear signs: Place “No Trespassing” signs at entrances and along boundaries. Check your state’s placement and size rules.
- Secure access: Use locks, gates, and lighting for after-hours closures.
- Issue verbal or written trespass warnings: If someone refuses to leave, state the request clearly and document it.
- Call law enforcement when needed: Do not escalate confrontations. Provide video or photos if available.
- Keep records: Incident logs, camera footage, and copies of warnings support your case.

For Individuals

- Respect boundaries: Do not enter posted or fenced areas. If asked to leave private property, do so promptly.
- Ask before entering: If you are unsure whether an area is open to the public, request permission.
- Resolve mistakes quickly: If you entered by mistake, leave immediately and cooperate.

How This Relates to Contracts

- Unjust enrichment can fill gaps when no enforceable contract exists but a benefit was conferred.
- When a valid contract covers the issue, courts often deny restitution and require parties to rely on their contract remedies instead.
- Related terms you may review: promissory estoppel (reliance-based enforcement), specific performance (court-ordered performance), lessor and lessee (landlord-tenant roles), material term, and contract formation.

## Summary Checklist

- Unjust enrichment basics: benefit conferred, knowledge or acceptance, unfair to retain without paying, and no adequate legal remedy
- Remedies: restitution of money, quantum meruit, and in some cases constructive trust or equitable lien
- Defenses to restitution: gift, volunteer/officious intermeddler, express contract covers the dispute, change of position, illegality
- Criminal trespass elements: unauthorized entry or remaining, notice (signs, fencing, locks, or owner’s request), and required intent level
- Trespass scenarios: after-hours entry, refusal to leave, posted or fenced property
- Owner steps: clear signs, secure access, documented warnings, call law enforcement if needed
- Individual steps: respect posted areas, leave when asked, seek permission where uncertain
- State law differences: confirm your state’s statutes and penalties before taking action

## Quick Reference

| Topic                                  | Elements (short)                                           | Typical Result                        |
| -------------------------------------- | ---------------------------------------------------------- | ------------------------------------- |
| Unjust Enrichment                      | Benefit conferred; knowledge/acceptance; unfair to retain  | Restitution or quantum meruit         |
| Criminal Trespass — Unauthorized Entry | Entered without permission; notice via signs/locks/fencing | Misdemeanor; fines; possible arrest   |
| Criminal Trespass — Failure to Leave   | Remained after being told to leave by owner/agent          | Misdemeanor; fines; possible arrest   |
| Trespass on Posted Property            | Entered fenced or clearly posted “No Trespassing” area     | Penalties may increase in some states |


Unjust Enrichment and Criminal Trespass: Definitions, Elements, and Case Examples