The Vatican has ordered the first ever external audit of its accounts as part of Pope Francis' efforts to reform the Roman Catholic Church.
The auditor, accounting giant PricewaterhouseCoopers, will start work immediately, a papal spokesman said.
Pope Francis has promised to make the Vatican's finances more transparent after a series of scandals.
Last year he created a new ministry to oversee papal finances, headed by Cardinal George Pell.
Cardinal Pell later said he had discovered millions of euros "tucked away".
While he did not say any wrongdoing had occurred, he added Vatican departments long had "an almost free hand" with their finances.
Turning to an external auditor puts the Vatican more in line with international standards.
PwC will review the Vatican's consolidated financial statements, spokesman Federico Lombardi said, which includes assets, income and expenses.
Author Gianluigi Nuzzi obtained secret recordings of Pope Francis this year suggesting the Pontiff had grown exasperated at vested interests in the Vatican.
"If we don't know how to look after money, which you can see, how can we look after the souls of the faithful, which you can't see?" he told clerics in 2013, the recordings said.