But the two blocs' weak performances in last September's election, when they both suffered their worst results since Germany became a republic in 1949, mean the latest incarnation of their awkward alliance promises to be the most fractious yet.
MEMBERS of Germany's Social Democratic Party (SPD) have voted in favour of a coalition with Angela Merkel's Christian Democrat (CDU) conservatives.
When the vote was counted on Sunday, 66.02-percent of the more than 450,000 SPD voting members approved the grand coalition, leaving only 33.98-percent opposed.
All that "requires us to begin work quickly in the government", she said.
In power since 2005, she has led Germany and the European Union through the financial and debt crises, but her waning authority at home could complicate efforts to deepen integration in the euro zone.
Its leaders have vowed to "hunt" Merkel, though so far AfD's novice lawmakers have stood out mainly by failing to grasp parliamentary procedures and putting forward motions all other parties reject.
The center-left Social Democrats voted overwhelmingly to remain in a coalition with Merkel's conservative bloc, after hard and drawn-out negotiations triggered by September's elections, which saw the rise of a new right-wing force in German politics and raised questions about Merkel's future.
To stop the SPD from leaving the coalition, Merkel must deliver on those points in the coalition deal that are most dear to the Social Democrats: healthcare reform and investment in education to meet the challenges of the digital age. Merkel was weakened by her decision in 2015 to welcome hundreds of thousands of people seeking asylum, which contributed to the rise of a far-right party that stole conservative voters.
Germany's second biggest party, the Social Democrats (SPD), on Sunday finally gave the all-clear to renew their partnership with Merkel's conservatives, ending a political impasse that had plagued the country since September's inconclusive election. Her party received the most votes but it took five months to form a coalition government. The CDU/CSU and SPD have governed in a grand coalition since 2013. "The SPD will be in the next government", said SPD's caretaker chairman Olaf Scholz, adding that his party plans to send three male and three women ministers to the cabinet. To quell the rumblings in her own party, Ms Merkel has brought in one of her biggest CDU rivals, Jens Spahn, as health minister.
Fiercely opposed to her open-door refugee policy, Spahn has advocated a sharp conservative shift to coax back voters from the AfD.
Had the long-time German leader faced a "no" result, she would have been left with only two realistic options: forming a minority government or seeking a new election.
Angela Merkel, also referred to as "Muttie" (mother) Merkel is still a popular choice in her country.
The German authorities will possibly be sworn by March 14.