Israeli Prime Minister Ehud Olmert handed in Sunday evening his resignation to President Shimon Peres in Jerusalem, after serving in the office for 33 months.
Earlier in the day, the premier told his cabinet he was planning on handing in his mandate, following the election last week of Foreign Minister Tzipi Livni as the new leader of his ruling Kadima Party.
"This is not an easy decision and not a simple one," Olmert said to his ministers, adding that "I think I am acting in a suitable, statesmanlike and responsible manner, as I promised the Israeli public."
The president, now given the official notification, will immediately begin consultations with the heads of Knesset factions before asking another legislator almost certain to be Livni to form a new government.
He is set to meet the leaders of the Kadima, Labour, Likud and Shas parties the main coalition partners on Sunday night.
Under Israeli law, Peres has one week to consult the Knesset faction heads.
Livni has said she hopes to be able to form a new government as soon as possible, but on Sunday afternoon it was far from certain she would be able to do so. Kadima, although the largest faction in parliament, has only 29 of the 120 Knesset seats, and Livni will have to negotiate with other parties in order to form a stable government.
She will have 42 days to complete the task, failing which new elections must be held within 90 days. Olmert remains caretaker premier until a new government is formed.
Olmert announced in July that he would quit the centrist Kadima party leadership, and then the premiership, because of multiple investigations against him for alleged corruption. Police recommended two weeks ago that he be indicted on some of the allegations.
He became prime minister after the March 2006 elections, but has faced growing criticism since the war with the Lebanese Hezbollah movement in the summer of that year.