The Civil Code recognizes unjustified enrichment as a violation of the law. And as for any misconduct, responsibility is provided for such behavior of the subject. 
Unreasonable enrichment: Civil Code of the Russian Federation
The legislation provides an interpretation of the concept under consideration. In particular, the definition is present in 1102 Art. Unjustified enrichment is the saving or acquisition of material assets at the expense of other persons without the grounds established by legal acts, laws or a transaction. This situation is quite common in entrepreneurship. In ch. 60 of the Code provides rules that are subject to application to such requirements as:
- Refund of an obligation in an invalid transaction.
- Claim by the owner of property from illegal alien possession.
- Indemnification including those caused by dishonest behavior of a person who has enriched himself at the expense of the victim.
Preconditions for misappropriation
Unreasonable enrichment may result from the recognition of a contract of sale, purchase, exchange and other, concluded between the parties, invalid or termination of the agreement at the initiative of one of the participants. The misappropriation is in the case when someone uses someone else's property (for example, a land plot). 
Unjust Enrichment: Judicial Practice
To form a clearer picture of such a phenomenon as misappropriation, it is advisable to consider an example. Suppose an entrepreneur, in accordance with the contract of sale of an immovable object and equipment, received ownership of the construction - a sawmill. The local administration filed a lawsuit about unjustified enrichment - illegal use of land under the building in the absence of authority and without payment.
The entrepreneur, in turn, insisted that the municipality could not collect payment from him after the conclusion of the contract. But the arbitration considered this argument insolvent. The mere fact of a transaction with the subsequent conclusion of an agreement does not give rise to property rights to the property before its registration. In this regard, until the completion of the mandatory procedure established by law, the entrepreneur is obliged to make payments for the use of land in accordance with the rules applicable to lease relations. The defendant did not provide evidence of the necessary amounts, therefore the requirements of the administration were satisfied. The entrepreneur was imposed the collection of unjustified enrichment. 
Effects
What threatens unjust enrichment? Under article 1104, all property that was obtained illegally is returned to the victim in kind. This rule applies if material values are preserved in the condition in which the acquirer appeared. Along with this, the law establishes liability for any, incidental, including deficiencies or deterioration of property acquired in an unlawful manner, which appeared after the defendant should or already became aware of its unjustified enrichment. Up to this point, he can only be punished for intent or gross negligence in handling the received values. For example, the buyer gave the supplier an advance. Upon termination of the agreement between them, the amount received is refundable.This is due to the fact that upon termination of the contract, one participant is not deprived of the right to demand the executed, if the other is enriched unreasonably. Thus, it turns out that the subject returns what he received in the same volume and condition. 
Important Nuances
Unreasonable enrichment provides for the accrual of interest for misuse of other people's money. This rule is effective from the moment when the acquirer should have learned or already learned about his illegal behavior. In this case, it is also important to remember that the provision applies to cases of misappropriation of money. There is another important point. It consists in the fact that when applying the consequences of the invalidity of a transaction executed by both participants, when one received a certain amount, and the other received a service, work or products, it is necessary to proceed from the equal amount of mutual obligations. The rules on unjustified enrichment can be applied if the amount of cash is clearly more than the value of the transferred property. 
Probable difficulties
As mentioned above, as a mandatory consequence, which entails unjustified enrichment, is the return of purchased in kind. However, this is not always possible. In such cases, the victim has the right to demand compensation for the actual value of the property, as well as losses relating to changes in its price, at the time of receipt, if the unscrupulous acquirer did not do this immediately after he became aware of the illegality of his actions. The inability to return values takes place in various cases. For example, the property may be absent from the acquirer, or it has practically lost its economic purpose due to complete depreciation and therefore can no longer be exploited by the owner.
Unintentionality
Suppose an entity illegally temporarily used someone else's property or services, not trying to take possession of it. In this case, the victim should reimburse everything that this person has saved, at the cost that existed at the time of the end of use and in the place where it was carried out. Such a rule is present in Article 1105 of the Code. When determining the value of unjustified enrichment, you can use the rule of Art. 424 on the application of the price that is charged for similar services, goods or work under comparable circumstances. 
Income from illegally acquired property
Unjustified enrichment, among other things, may be accompanied by a certain profit from material assets obtained in an unlawful manner. In accordance with the law, an unscrupulous acquirer is obliged to return to the victim all the income that he derived or should have extracted from the property. For example, immovable objects owned by the state were included in the authorized capital, and the state owned economic management law.
The presence of these rights allows you to recognize the transaction as invalid. In this case, real estate is subject to return to the rightful owner and owner. The state-owned enterprise appealed to the court with a demand for reimbursement of interest for the use of other people's funds. The argument was the fact that the defendant throughout the entire period of illegal possession entered into leases. Without the appropriate rights, the company used the property obtained illegally for entrepreneurial purposes and made a profit. According to the applicant (state-owned enterprise), the funds received from leasing the objects should be recognized as unjustified enrichment and collected in favor of the owner according to the law. 
However, considering these arguments and analyzing the situation, the competent authority came to the conclusion that the defendant could recover exactly the income that he derived from the operation of the facilities, but not the rent itself.The court motivated its decision by the fact that non-residential construction requires certain maintenance costs. If the applicant leased it, he himself would also have borne the corresponding costs. Thus, the defendant could not get rich solely on rent without incurring the necessary costs. As a result, the amount of net profit (income minus expenses) may be recovered from it in favor of the state-owned enterprise that is the legal owner of the immovable object.
