Abstract: The subject of the study is the main issue of distinguishing a civil tort from a criminally punishable theft in the case of appropriation of a found thing. The study attempts to resolve this issue taking into account the position of the Constitutional Court of the Russian Federation, expressed in the resolution adopted in 2023, as well as taking into account current trends in the formation of law enforcement practice and scientific positions. Two main situations related to the legal assessment of the acquisition of property by a person who has left the owner's possession against his will are analyzed: 1) the secret possession of someone else's thing by a person who observed its loss by the owner and had a real opportunity to immediately inform the owner of the loss or return the thing to him; 2) the seizure by a person of the property found by him, when the circumstances of the loss of this property from the possession of the owner are not known to him. The issue is being considered on the basis of a comparative legal and systematic analysis of the provisions of civil legislation regulating the procedure for handling a find, and the norms of criminal legislation establishing liability for theft. In analyzing the main problem, the classification of found property developed in the doctrine of criminal law was used and, taking into account the formal legal method, an assessment of the facts of its seizure was given. As a result of the conducted research, the approach is justified that taking possession of a find does not qualify as theft of property if there are three necessary conditions: the absence of individually defined signs in the property, according to which the owner of the property can be identified; the person who discovered the find does not take active actions to seize it until the final termination of ownership of the thing has been definitively terminated, which is reliably known to the person who discovered the find (for example, it is located in a place unknown to the owner (or another owner), or the thing is abandoned, which the owner refused, which is reliably known to the person who discovered the find. The stated provisions will allow law enforcement officers to unambiguously resolve the issues of qualification of those acts that form signs of theft in cases of illegal seizure of found property and its conversion in their favor or in favor of other persons.