The question concerning the concept of the subject matter of the claim, which is one of the features that individualize the claim, is one of the most disputable and unsettled in the doctrine devoted to the claim. A number of legal scholars define the subject matter of the lawsuit as the substantive law claim of the plaintiff against the defendant. However, this definition cannot be accepted as correct, since, first, petitioners bring claims that cannot meet the above requirement (for example, claims for recognizing transactions as invalid), and, second, the statements of claim filed with the court contain demand (request) for the court, rather than a claim against the defendant.According to another point of view, the subject matter of the claim should be understood as the subjective right indicated by the plaintiff and the corresponding obligation or civil legal relationship in general, about which the court must make a decision. It is also impossible to agree with the above definition of the subject matter of the lawsuit in view of the fact that, as A. A. Dobrovolsky correctly noted, the law provides that the statement of claim must indicate the plaintiff’s claim rather than the disputed legal relationship. We should also agree with the argument given by G. L. Osokina, according to which the logic and practice of the statement of claim for the defense dictate the need to include a subjective right or legitimate interest in the basis of the claim, and not in its subject matter. According to the point of view of K. S. Yudelson, the subject matter of the claim is the requirement to the court to protect the right in the form that corresponds to the stated requirement. However, since this definition is too general, it cannot be used to resolve the issue of the equivalence of claims. The definition of the subject matter of the claim as protection (V.N.Scheglov) or a method of protecting the right (G.L. Osokina) also have the similar drawback. The most correct is the definition of the subject matter of the claim as the protection of a subjective right, freedom or legitimate interest through the specific application of one of the methods provided for by law or the direct exercise of the right that the plaintiff asks the court about.