The article focuses on the main similarities and differences regarding the concept of the penalty clause and the manner in which it is exercised in the Polish and Spanish legal systems. The aim is to conduct an analysis of selected issues relating to penalty clauses (contractual penalties), in particular their characteristics, the relationship between the claim for payment of contractual penalty and the occurrence of damage, as well as establishing a contractual penalty for withdrawal from a contract. The views of representatives of the judiciary and the role of the judge in shaping the concept of the penalty clause in both jurisdictions, in particular as regards moderation of contractual penalties, will also be analyzed.