The approximation of the law of the Czech Republic with Community law took place in the conditions of CR association with EC defined by the European Agreement, establishing the association between the Czech Republic and the European Communities and their member states, which entered into force on l February 1995. The preparation of the Czech Republic for its entry to EC/EU was governed by the Programme of CR Preparation for EU Membership, drafted and updated by the Government of the CR in 1999 and 2000 respectively. The details of preparatory activities are reported. In the course of CR association with EU also the constitutional background of CR entry in EU was assured. Art. 10a of the Constitution of the Czech Republic makes it possible to transfer some sovereign powers of CR organs to an international organization or institution by an international treaty and the new wording of Art. 10 provides that the promulgation of such an international treaty ratified by the Parliament forms part of the national legal system and is superior to laws.With regard to the accession of CR to EU (on l May 2005) the procedural rules of both the Chamber of Deputies and of the Senate were so amended as to enable the CR Parliament to join effectively in the decision-making of EU organs, in particular the Community legislation. Also new Methodological Instruction of the Government for the assurance of the works related to the fulfilment of the obligations arising from CR membership in EU were adopted (on 12 October 2005). In conclusion the author points out some problems of the relation of national legislation and EU legislation. Community legislation is obviously rightly criticized for its fragmentary character and insufficient flexibility due to inconsistent application of the principle of subsidiarity. The legal system of EU requires the codification of its fundamental legal principles and vast simplification and purification of its legal regulations. In this respect the draft of the European Constitution, regardless of its further fate, has brought about a number of proposals for the division of legislative competences between the Union and its member states as well as for effective participation of member states in the making of Community law in accordance with the principles of subsidiarity and proportionality.