It seems indisputable, that every single professional lawyer perfectly knows the rule clara non sunt interpretanda. This principle constitutes not only the subject of legal doctrine’s great interest, but also a very relevant point of numerous courts’ judgments. However, despite its vital role, the understanding of this principle is much diversified and the disputes about its meaning go on for many years. Particularly, this principle is nowadays getting more often contrasted with the rule omnia sunt interpretanda. The authors of this article aim at providing the answer to the question about the essence of this principle and at providing all arguments supporting the idea to implement it in the legal practice. Simultaneously, it seems indispensable to point out several unquestionable disadvantages connected with this rule