European capitals will be watching closely since, whatever the result, there is likely to be a change from outgoing technocratic premier Mario Monti's agenda of austerity and economic reforms.
The most likely winner is centre-left leader Pier Luigi Bersani who says he will stick to Monti's budget rigour but also create more growth and jobs as Italy endures its longest recession in 20 years.
But the scandal-tainted Berlusconi, a three-time prime minister who is also a defendant in two trials for tax fraud and having sex with an underage prostitute, could come a close second.
With his showman interview skills, Berlusconi has taken to the airwaves for two months straight and has risen sharply in the polls with a promise to reimburse Italians an unpopular property tax.
He has also won votes by blaming a "hegemonic" Germany for Italy's woes.
The final day of campaigning was on Friday and candidates on Saturday were supposed to stay silent on the eve of the vote but Berlusconi apparently broke the rules by speaking to journalists.
In an interview with Greek television that was reported by Italian media, Berlusconi said: "I contradicted the lords of austerity who are now trying to get rid of me."
He said Monti was "subservient and always on his knees in front of Mrs Merkel (German Chancellor Angela Merkel) and now she does not want to lose him".
"I would give her a run for her money," he said.
The real wild card of the vote is Beppe Grillo, a boisterous former comedian turned grassroots campaigner who has channelled growing social discontent in Italy and could come third.
Polls indicate the result may not give Bersani alone a strong enough majority to rule and he may have to seek an alliance with Monti, which could bring the former Eurocrat back into government.
Polls open at 0700 GMT and close at 2100 GMT on Sunday and open again for a second day of voting at 0600 GMT on Monday and close at 1400 GMT.
Exit polls are expected immediately after that and preliminary official results will begin trickling through later on Monday and perhaps into Tuesday.
Officials have called on Italians to vote amid fears that general disenchantment with politicians could mean a much lower turnout than usual.
Forty-seven million Italians are eligible to vote.
Complex electoral laws mean the rules are different for the composition of the lower house, the Chamber of Deputies, and the upper house, the Senate.
While Bersani is expected to win a majority in the lower house, he may struggle in the upper house.
A coalition between Monti and Bersani would not be simple because of the differences between the free-marketeer Monti and a small far-left party that is already in coalition with Bersani.
Berlusconi was forced out in November 2011 following a parliamentary revolt, a myriad of sex scandals and a wave of panic on financial markets.
The sober Monti, a former economics professor, has brought the markets to heel and restored Italy's image as a key player in the eurozone debate.
Italy is the euro area's third largest economy after Germany and France and a major exporter.
While its debt is sky-high at around 120.1 percent of its gross domestic product (GDP) -- second only to Greece's -- its public deficit is under control.
European Parliament president Martin Schulz, a German once invited by Berlusconi to play the role of a Nazi camp guard, has urged Italians not to vote for him.
"Berlusconi has already sent Italy into a tailspin with irresponsible government action and personal capers," Schulz told the Bild newspaper.
German Finance Minister Wolfgang Schaeuble meanwhile told the Stuttgarter Zeitung that it was "in Italy's interests" to continue Monti's reforms.