The modern concept of plagiarism is grounded in assumptions such as the ownership of ideas, authors’ rights, and individual originality—assumptions that cannot be readily projected onto the literary and rhetorical traditions of ancient Greece and Rome. Adopting a historical–conceptual approach, this article seeks to demonstrate that what was discussed in antiquity under the rubric of theft or appropriation did not concern the seizure of ideas or themes, but rather the improper use of another’s expression, style, and mode of discourse. Within this framework, imitation (mīmēsis / imitation) was not regarded as a reprehensible practice; on the contrary, it constituted the core of educational, rhetorical, and literary systems and was considered a necessary condition for the formation of the orator and the poet. By examining Greek writings on inventions, pseud-epigraphy, literary criticism, and educational treatises, and subsequently analyzing the views of Roman theorists, the article shows that the boundary between legitimate imitation and literary theft in the classical tradition is aesthetic and ethical rather than juridical. Finally, by focusing on style, authorial intention, and creative reworking, the article argues that “plagiarism” in antiquity was understood less as a violation of intellectual property than as a failure of creative imitation and an inability to achieve expressive individuality