During the discussions on the adoption of new provisions o the Polish Constitution of 1997 relating to Poland's membership in the European Union numerous dilemmas have arisen regarding both the subject of possible regulation and forms of presentation of new principles and procedures. The authoress only points to those problems that are likely to be disputable and controversial. Among them is, first of all, the description of EU in the constitution, i.e. a particular constitutional 'definition of the Union'. The author examines arguments for and against such a legislative solution and provides its analysis based on similar provisions of the constitutions of other member states (especially Article 23 of the Basic Law of the Federal Republic of Germany). She does not confine herself to an analysis of the provisions of the constitution, but also considers the purpose for insertion of provisions of such type in constitutions. In this respect, she refers to the jurisprudence of constitutional courts. The judgment of the German Federal Constitutional Court on the Treaty of Lisbon provides an example. In this judgment, the Court applied Article 23 of the Basic law as a constitutional criterion of conformity of the treaty with the German constitution. In this context, the authoress examines the issue of a formal classification of the Union as legal entity, an international organization, union of states, etc. as well as its relation with a federation model. The second issue discussed in this article is the principle of equality of member states in the European Union and, especially, whether we can recognize it as a principle underpinning the Union. The authoress provides the examples of those constitutions which expressly formulate such principle with the aim of proving that they consider that principle, above all, as equal rights and obligations to determine the fundamental principles governing the functioning of the Union and making its basic decisions. Moreover, this approach is not undermined by the use a qualified majority vote and unequal participation of member state e.g. in the composition of the European Parliament. Another controversial issue is whether we can recognize that EU member states transfer specific powers to the EU level to be jointly exercised. As we can see, most of the constitutions of member states treat the aim of such delegation in this way, confirming the maintenance of sovereignty, also because this does not mean the transfer of powers to a particular separate third party. This approach is not undermined by the exercise of powers by the institutions of the Union. The final issue deals with implementation of EU law. In our country, it is a particularly 'sensitive' issue, because Poland is one of the EU member states that are lagging behind in the implementation of the directives. Consequences of this fact affect not only the political and economic spheres, but also the prestige of the state and the rights of its citizens. Therefore, the question arises whether the constitution might contain any provisions to prevent this situation from occurring. In the Polish context, this relates to the need for introduction of new legal instrument by the government in the form of regulations having the force of a statute.