Whether Angela Merkel and the CDU, or Martin Schulz and the SPD no party is likely to emerge with an absolute majority. Here's an overview of who might go with whom for the next government.
Once the campaign dust has settled on every German election, either at state or national level, the political parties, who have spent the previous months pulling apart each other's policies and casting aspersions on the credentials of each other's candidates, have to find a way to make friends.
These tortuous negotiations can take several weeks and culminate in a "coalition contract" that sets out the political agenda, including specific legislative goals, that will determine the next few years.
The parties take these agreements very seriously - but they also occasionally provide a good excuse to break campaign promises: "Sorry, our partners wouldn't allow that into the deal!"
Below are the most common options, with a few caveats regarding coalition-willingness: the right-wing nationalist Alternative for Germany (AfD) is currently seen as a pariah for all the other parties, both at state and national level, while the other parties have so far only found the stomach to accommodate the socialist Left party in some states.
"Grand" - Black-Red: Christian Democratic Union (CDU) and Social Democratic Party (SPD)
Grand coalition usually means the standard alliance of Germany's two biggest, centrist parties - the two parties that most Germans consider safe options for a competent government. It's the coalition that Chancellor Angela Merkel currently presides over at a federal level, and the one she has run in two of her three tenures. Almost all the German states have seen this combination in charge in their history, though at the moment, only Saarland currently has it.
The problem that the grand coalition usually represents for the Social Democratic Party (SPD), however, is that it is both forced to accept the CDU's authority in the two key government offices - the chancellery and the Finance Ministry - but then also struggles to present itself as a viable alternative when election campaigns come around. The old argument: "What can you offer? You've been in power all this time!" always stings.
Black-Yellow: CDU and the Free Democratic Party (FDP)
Germany's natural center-right coalition has governed Germany at a federal level for the bulk of its post-war history. The last time was under Merkel from 2009 to 2013, but before then, CDU Chancellor Helmut Kohl led no fewer than five black-yellow cabinets from 1982 to 1998.
It's easy to see why the combination appeals to so many Germans: the CDU stands up for Germany's Christian white conservative middle classes, while the FDP brings in the young business-friendly, free market entrepreneurs that populate the cities. But the failures of the FDP in recent years has taken this card off the table for now (the FDP is currently polling at between 6 and 7 percent nationally), and this particular combination is not in charge of any German state at the moment.
Red-Green: SPD and Green party
This is the standard make-up for a center-left government in Germany - most successfully led by SPD Chancellor Gerhard Schröder from 1998 to 2005. But it has fallen out of favor since the charismatic duo of Schröder and Foreign Minister Joschka Fischer were around, and there is currently little likelihood it will take over after the parliamentary election on September 24: the SPD is struggling to poll over 30 percent, while the Greens are languishing at around 8 percent.
Nevertheless, they have made very happy bedfellows in the past: the SPD is traditionally supposed to catch the "old-left" supporters, the working classes and trade unions, while the Greens are the natural party for the progressive leftist metropolitan voters. But that formula hasn't worked in the last few years, not least because Red-Green ditched its leftist roots in 2003 and embraced neo-liberal labor reforms ("Agenda 2010") in order to catch the business-centric center - and has forfeited some of its base to the Left party.
Red-Red-Green: SPD, Left party, and Green party
Since a center-left option is not currently likely, the SPD and the Green might just be able to hold their noses and offer a berth to the socialist Left party. Until now, that option has not been mooted at a national level, partly because of the lingering connection of the Left party with the East German dictatorship (though time is gradually removing this from the list of concerns), and partly because of the Left's occasionally populist rhetoric about leaving NATO - which the other parties fear will scare of Germany's middle class base.
However, Red-Red-Green's electoral success in the German capital last September (and in Thuringia in 2014 under the leadership of the Left party) has at least turned it into a possibility at a national level. But liberal Berlin, with its old-school leftist eastern districts, probably has more stomach for this combo than Germany at large. Nevertheless, given the polling weakness of the Greens, this is likely to be Schulz's only option, if he wants to be chancellor.
"Jamaica" (Black-Yellow-Green): CDU, FDP, and Green party
Of Germany's major leftist parties, the Greens are the most likely to appeal to Germany's conservative center - or at least the party least likely to disturb their center-right pro-business plans, since its traditional electorate does not comprise working class voters.
Though it has never made up a national government, Jamaica coalitions have governed one state - Saarland from 2009 to 2012 - and a number of local district councils. It is also currently being mooted as a possibility in the state of Schleswig-Holstein, following the CDU's success there in the May 7 election. However, if the Green leaders make any such deal, they'd have to persuade their party members, who are generally of a more leftist bent, and would prefer a so-called "traffic light" coalition.
"Traffic light" (Red-Yellow-Green): SPD, FDP, and Green party
In this coalition, the yellow light is likely to feel out of place: the free-market-friendly FDP can legitimately fear being overwhelmed as it is wedged between its leftist partners of the SPD and the Greens. While the SPD and the Greens are usually willing to accommodate a junior partner who is unlikely to cross their main plans and yet still put them in power, the FDP generally rules this one out.
Indeed, former FDP leader Guido Westerwelle consistently refused to entertain the notion at a national level, on the grounds that their platforms were too different, while Wolfgang Kubicki, party leader in Schleswig-Holstein, has already virtually done so in his state following May 7. Traffic light negotiations have often fallen apart in other states in the past - notably in Berlin in 2001 and North Rhine-Westphalia in 2010. Then again, one traffic light was successfully turned on last year in the western state of Rhineland-Palatinate.
"Kenya" (Red-Black-Green): SPD-CDU-Greens
As ideas go, a Kenya coalition (sometimes even called the Afghanistan coalition, seeing as that troubled state's flags features the same colors) seems like a sound option: the SPD and the CDU represent Germany's solid center, and the Greens are an unthreatening third party, happy to take over the Environment Ministry.
Whether called "Afghanistan" (flag above) or "Kenya," the Red-Black-Green coalition combination arises infrequently
But then again, given that the SPD and the CDU usually gain more than 50 percent of the vote, it's rarely an option that is called upon. So far, it has only come to pass in one state: last year in Saxony-Anhalt, when the SPD's vote collapsed, and the AfD took a quarter of the votes. It turns out that uncooperative electorates sometimes force parties to improvise.