Following the European Council’s political decision to open negotiations and to convene the bilateral Intergovernmental Conference on accession, negotiations were formally opened on 3 October 2005 at the first session of the Intergovernmental Conference between EU Member States and the Republic of Croatia, where the exchange of General Positions of the European Union and the Republic of Croatia took place.

The formal opening of the negotiating process is followed by the analytical overview and evaluation of the degree of harmonisation of national legislation with the acquis communautaire, known as screening. The main purpose of the screening process is to determine the differences that exist between the national legislation and the acquis communautaire for every chapter with which the national legislation needs to be harmonised by the date of accession. On the basis of the conducted analysis, the candidate country is required to state whether it will be able to fully harmonise national legislation with the acquis communautaire in individual chapters or if it will require transition periods for complete harmonisation with, and implementation of, the acquis communautaire. Screening is conducted for every chapter individually. The duration of the screening process for individual chapters depends on the extent and the amount of the acquis communautaire for the respective chapter and can last from one day to several weeks. Overall, the screening process usually lasts for a year.

After screening is completed, the decision on the opening of negotiations for individual chapters, depending on the evaluated readiness of the candidate country, is made by the Member States within the Council of the European Union. With the opening of negotiations for individual chapters, the substantive phase of the negotiations begins. During this phase, the subject of negotiations is the conditions under which the candidate country will adopt and implement the acquis communautaire in the respective chapter, including transitional periods which the candidate country might have requested.

Negotiations are conducted on the basis of the negotiating positions of the European Union and the candidate country which are prepared for each negotiating chapter after the screening results (see Negotiating positions).

During the whole negotiating process, the European Parliament and the National Committee for Monitoring the Accession Negotiations of the Republic of Croatia to the European Union are regularly briefed on the course of the negotiations and the progress made.

After agreement has been reached between the EU and the candidate country on the individual chapter of the negotiations, and once the set benchmarks have been met, the respective chapter is considered temporarily closed.  The formal decision is made by the Intergovernmental Conference at ministerial level.   If, before the Accession Treaty has been concluded, new provisions for a specific chapter of the acquis communautaire are adopted, or if the candidate country does not meet the set benchmarks or obligations assumed under the respective chapter, negotiations for the chapter in question can be reopened.

Accession into full membership

When the negotiations for all chapters of the acquis communautaire have been temporarily closed, the European Council, in its conclusions, usually marks the end of the negotiation process with a candidate country. The results of the negotiations are then incorporated in the provisions of the draft of the Accession Treaty which is drawn up jointly by representatives of the EU Member States, representatives of EU institutions and representatives of the candidate country.

After agreement has been reached on the text of the Accession Treaty between the EU and the candidate country, the draft of the treaty is referred to the EU institutions, EU Member States and the candidate country where appropriate procedures regarding the ratification of the document take place.  

Prior to the signing of the Accession Treaty, the European Commission needs to deliver its final opinion on the application for membership of the candidate country on the basis of the draft Accession Treaty. Additionally, the European Parliament needs to give its consent and, finally, the European Council must reach a unanimous decision on acceptance of the new candidate country and its application for EU membership. From that moment on, the candidate country is regarded as an acceding country.

The Treaty is signed by the highest officials of the EU Member States and the acceding country. The document is then referred to signatories for ratification in accordance with their domestic constitutional provisions.

Following the signing of the Accession Treaty, the acceding country has the right to participate in the work of the European Council and the European Parliament as an active observer.

In order to enter into force, the Accession Treaty needs to be ratified by the national parliaments of the EU Member States and the parliament of the respective acceding country. Prior to the ratification of the Accession Treaty by national parliaments, most of the acceding countries hold a referendum by which it allows its citizens to make a final decision on the accession of the country in question to the European Union.

The acceding country becomes a member of the EU with the entry into force of the Accession Treaty, usually on a predetermined date, under the condition that the ratification process has been finalised.