The European People's Party (EPP), the largest political group in the European Parliament which currently holds 182 out of 751 seats, will start its election convention at Zagreb Arena sports venue on Wednesday. The group's new leader is set to become the outgoing head of the European Council, Donald Tusk of Poland, replacing Frenchman Joseph Daul who chaired the group since late 2013.
Over 2,000 delegates from 40 countries are also due to discuss a climate action plan, youth policies and the Western Balkans.
The EPP's first congress in Croatia will be attended by heads of state and government and senior officials from European centre-right parties.
Apart from Tusk, among those attending will be the outgoing Commission President Jean-Claude Juncker and his successor Ursula von der Leyen, German Chancellor Angela Merkel, Austrian Prime Minister Sebastian Kurz, the prime ministers of Bulgaria, Greece, Ireland, Latvia, Moldova, Romania and Norway, and the presidents of Switzerland and Cyprus.
Also present will be Italian, Slovenian and Ukrainian opposition leaders Silvio Berlusconi, Janez Jansa and Yulia Tymoshenko.
The EPP has not invited Hungarian Prime Minister Viktor Orban because his Fidesz party was suspended in March for violating democratic standards.
This alliance of European conservative centre-right parties was founded in 1976 and brings together 84 parties from 43 countries. With 182 of the 751 seats in the European Parliament won in May's elections, it is the largest political group in the European Union's legislature.