EU leaders on Thursday agreed to open talks with Bosnia on joining the bloc, though negotiations will only begin in earnest once the Balkan country has passed more key reforms.
"Congratulations! Your place is in our European family. Today's decision is a key step forward on your EU path," European Council head Charles Michel wrote on X, as leaders met at a Brussels summit.
"Now the hard work needs to continue so Bosnia and Herzegovina steadily advances, as your people want."
Bosnia has been an official candidate for membership since 2022 but needed to implement a string of reforms before getting the green light on progressing to the next stage.
Brussels last week said the country had completed some of the steps required, but outstanding judicial and electoral reforms remain.
Russia's war on Ukraine has reinvigorated the EU's drive to enlarge in eastern and central Europe, with its current member states agreeing in December to start talks on joining with Ukraine and Moldova.
The drive for new members is part of an effort to push back against Russian and Chinese influence in the EU's backyard.
German Chancellor Olaf Scholz posted his congratulations for Bosnia on X and said it was "a clear sign in favour of a strong Europe".
Italy's government also hailed the "historic decision" and said it sent a clear signal to the Balkan nations looking to join the bloc.
Launching negotiations only puts Bosnia at the start of a long process of further painstaking reforms that usually last for many years before a country finally joins the EU.
Bosnia's regional neighbours North Macedonia, Montenegro, Serbia and Albania are already ahead in their efforts to join, but all remain far from membership.
Von der Leyen said Bosnia was now "fully aligned" with the EU's foreign and security policy, was improving its management of migration flows, and adopting laws to combat both money laundering and terrorist financing.
She welcomed its agreement to include in domestic criminal records the judgements of the International Criminal Tribunal for the former Yugoslavia.
And she noted further steps towards dialogue and reconciliation in the wake of the country's 1992-1995 war, with the creation of a new peace-building committee.
At the same time as they gave the thumbs up to Bosnia, the EU leaders urged Brussels to move ahead "swiftly" towards the next step of starting talks with Ukraine and Moldova.