The three parties have already held several rounds of "exploratory" talks to form a government since the center-left Social Democrats emerged as the largest party in Germany's election last month.
SPD party leadership on Friday voted unanimously to go-ahead with formal coalition talks, the Greens and FDP are scheduled to hold similar party votes on Sunday and Monday respectively.
The Christian Democratic Union of Konrad Adenauer, Helmut Kohl, and Angela Markel must regain its strength in the interest of the Federal Republic of Germany and the international community.