About 3.35 million registered voters will elect five presidents and 14 prime ministers in the nation's complex political system. Leading Serb, Croat and Muslim Bosniak parties campaigned on nationalist ticket in the run up to the vote.
Bosnians go to the polls on Sunday to decide if their country will pursue a path towards European Union membership and NATO integration or sink deeper into ethnic strife and further fragmentation.
More than two decades after a war in which 100,000 were killed, leading Serb, Croat and Muslim Bosniak parties are campaigning on nationalist tickets, reviving wartime pledges in programmes that fail to offer any clear economic or political visions.
About 3.35 million registered voters will take part in the presidential and parliamentary elections, choosing members of Bosnia's tripartite inter-ethnic presidency, consisting of a Bosniak, a Croat and a Serb, and lawmakers for parliament's lower house.
They will also select leaders and assemblies of its two autonomous regions - the Serb Republic and the Bosniak-Croat Federation, and of the Federation's 10 cantons.
In the run up to the vote, ethnic leaders spread fear using divisive rhetoric reminiscent of the war.
Campaigning has been marked by an unprecedented spate of violations, abuse of public funds and hate speech, monitors said..
Polling stations will close at 7 pm (0500 GMT). The first preliminary results are expected at midnight.
Bosnia and Herzegovina go to the polls on Sunday. But voters don't have an easy task since the country has one of the most complicated systems in the world pic.twitter.com/vy9uK65sK9— TRT World (@trtworld) October 6, 2018
Nearly 7,500 candidates are running for 518 offices, reflecting a massive and complex government structure based on ethnic quotas, designed under a peace deal that ended the country's 1992-95 war.
Experts say Bosnia cannot progress with such a large administration, but any attempts to change the constitution –– an integral part of the US-brokered Dayton peace accords –– have been obstructed by Bosnia's rival ethnic groups.
The ruling nationalist parties want to preserve the system of patronage under which an estimated one million of their party affiliates are employed at different layers of government, cementing electoral loyalties.
Such politics have driven about 170,000 educated people out of the country over the past five years, draining Bosnia of its young and threatening economy.
Pandora's box of divisions
The Serb and Croat presidential candidates, Milorad Dodik and Dragan Covic respectively, who are supported by their respective 'parent states' Serbia and Croatia, are set to further weaken Bosnia if elected, analysts say.
Pro-Russian Dodik has repeatedly advocated secession of the Serb Republic and integration with Serbia, while Covic has called for the creation of a separate Croat-run region.
"If current parties remain in power, a Pandora's box of territorial divisions will open which may lead to disintegration of Bosnia," said Zarko Papic, the director of the "Initiative for Better and More Human Inclusion" non-government agency.
In the event that Dodik's and Covic's parties lose some power, integration with the EU at least might go forward, said Florian Bieber, professor of Southeast European Studies at the University of Graz.
If elected, Dodik, who is under US sanctions for obstructing the peace accords, will work to transfer powers from the Council of Ministers, which is the de facto national government albeit with weak powers, to the presidency, whose main task is foreign policy.
"This is the first thing I'll do," Dodik told Reuters in an interview last week.