Welcoming the participants, the chairman of the summit, Croatian President Stjepan Mesic, said European Union enlargement was the only way Europe should go.
The integration of Europe is a unique, millennium endeavour which has no alternative and which needs to be completed in the interest of European countries as well as the whole world. European integration must neither be brought into question nor stopped, said Mesic.
He added the successful continuation of European integration called for an intensive campaign of informing citizens, not only in EU member states, but also in candidate states and those yet to obtain candidate status, so that the widest European public could become aware of the advantages of integration.
EU membership candidates as well as states aspiring to win candidate status must resolutely continue adapting to European standards and adopting European criteria in order to meet candidate status criteria and launch full membership negotiations as soon as possible, said Mesic.
He added that individual achievements in the process would be evaluated individually, with the application of equal criteria and setting of equal conditions for all potential EU member states.
Mesic said the adjustment of all in Europe to enlargement called for coming out of narrow national frameworks and renouncing the jealous preservation of what separates and differentiates.
Instead, we must aspire towards transforming national differences into a general European heritage and subordinating the narrow national interest, without renouncing its realisation, to the wider interest of integrated Europe, said Mesic.
He added that in seeking answers to the challenges which European countries and their citizens are faced with, one should not accept the limiting of the existing liberal model.
Speaking of issues in the fight against global terrorism, Mesic said that all European countries must resolutely and actively support it, in full cooperation with the United Nations, as well as pay special attention to the protection and respect of both human rights and benefits applied in the flow of people and commodities within the realisation of the European integration concept.
Forces inclined towards totalitarianism must not be allowed in any case or anywhere to use the fight against global terrorism as a front to limit democratic rights and freedoms, said Mesic.
The two-day 12th annual summit of regional presidents will pool 15 heads of state, although several have not yet landed in Zagreb due to fog but are expected in the morning.
After Mesic's speech, the summit will be addressed by Croatia's Parliament Speaker Vladimir Seks and Prime Minister Ivo Sanader.
Mesic will also give a talks at a plenary session on how to complete the European integration process, after which the participants in the summit will speak on the principle of seniority.