Why is the position vacant?
Caretaker Prime Minister Matteo Renzi resigned last week after losing a referendum on constitutional reform.
His plans were voted down by 59% to 41%, prompting him to honour a pledge he had made to stand down.
What now for Gentiloni?
After formally receiving the mandate from Mattarella, the 62-year-old former journalist will begin consulting with political groups to form a government.
Renzi’s Democratic Party (PD) has a majority in both houses of parliament.
However, the PD itself is severely divided between Renzi backers, like Gentiloni, and opponents.
He will report back to Mattarella on his progress in rallying support.
If he cannot form a government, Mattarella could ask someone else to try.
If, however, Gentiloni is successful, a new government could be installed within days.
All Italy’s major parties have called for elections as soon as possible.
However, before any vote can be held, the country needs a new electoral law to replace one that applies only to the lower house.
This could be declared illegitimate in January by Italy’s constitutional court.
The legislature is due to carry on until 2018.
However, early elections could be called at any time after parliament rewrites the electoral law.
The legislature is due to carry on until 2018, but early elections could be called at any time after parliament rewrites the electoral law.
A banking crisis?
Italy’s next prime minister will immediately face a crisis in the banking sector.
The country’s third-largest lender, Monte dei Paschi di Siena, may need state intervention to avoid collapse.
Did you know?
Italy has had 63 governments in the last 70 years.