Chairpeople: Angela Merkel(CDU), Horst Seehofer (CSU)
Parliamentary leader: Volker Kauder (CDU)
Voters: People over the age of 60, churchgoers, living in rural areas - especially in southern Germany - still represent the hardcore of CDU and CSU voters. The CDU has also traditionally done well among small business owners and people with lower or medium education levels.
2017 Bundestag election result: 33 percent (246/709 seats)
History: The CDU was founded in West Germany in 1950 in the aftermath of World War II as a gathering pool for all of Germany's Christian conservative voters. It became the most dominant political force in the post-war era, unifying Germany and leading the government for 47 of those 67 years, alongside its Bavaria sister-party, the Christian Social Union (CSU).
CDU Chancellor Konrad Adenauer, who governed from 1949 to 1963, is the closest the Federal Republic has to a founding father. It was Adenauer and his economy minister (and successor as chancellor), Ludwig Erhard, who presided over West Germany's "economic miracle." The party's reputation as Germany's rock of moral and economic stability continued under another long-term CDU chancellor, Helmut Kohl, who drove German reunification in 1990 - a key historic moment important in understanding today's politics.
Platform: Angela Merkel represents both a continuation and a break from the CDU's traditional values. Alongside Finance Minister Wolfgang Schäuble, German voters trust her to steward the economy safely. She also maintains certain conservative social values, such as opposition to same-sex marriage (though she voted against it herself, she ushered in gay marriage at the end of the last legislative period by sanctioning a conscience vote in the Bundestag). However, her relatively liberal stance on immigration has turned much of the CDU base against her.
Preferred coalition partners: FDP, SPD - and now the Greens
Social Democratic Party (SPD)
Chairperson: Martin Schulz
Parliamentary leader: Andrea Nahles
2017 Bundestag election result: 20.5 percent (153/709 seats)
Voters: The SPD has traditionally been the party of the working classes and the trade unions. The SPD's most fertile ground in Germany remains in the densely-populated industrial regions of western Germany, particularly the Ruhr region in North Rhine-Westphalia, as well as the states of Hesse and Lower Saxony.
History: The SPD was founded in 1875, making it Germany's oldest political party. In the tumultuous first decades of the 20th century, the party acted as an umbrella organization for a number of leftist movements, trade unionists, and communists. But with the founding of the Communist Party of Germany (KPD) in 1919, the SPD became the permanent home of the social justice reformers, rather than the revolutionaries - though that didn't stop its politicians from being sent to concentration camps during the Third Reich.
The SPD's first chancellor, Willy Brandt, governed West Germany from 1969 to 1974. He earned an international reputation for reconciliation with Eastern Europe during his time as foreign minister in a CDU-led coalition government. He was succeeded by Helmut Schmidt, an SPD icon until his death in 2015. Both remain hugely respected figures in German politics. Altogether, the party has been part of the German government for 34 of the 67 years of the Federal Republic and led governing coalitions for 21 of those. Though its reach has eroded significantly in the past few years, it was still behind some of Merkel's most significant social reform policies during her third government, which has just ended.
Platform: The SPD's best suit has always been social policy. It stands for a strong social infrastructure, though it also advocates sanctions-based unemployment benefits. In 2015, the SPD was instrumental in introducing a national minimum wage in Germany - currently 8.84 euros ($9.40) an hour.
Nevertheless, the Agenda 2010 labor market reforms introduced by SPD Chancellor Gerhard Schröder in the early 2000s has lost the party some traditional support, and it's no accident that Martin Schulz's candidacy was marked by a "correction" of the policy, and a new emphasis on social justice and tax redistribution - though that failed to help him.
Preferred coalition partners: Greens, CDU - the Left, but only at state level.
The Left party (Die Linke)
Color: Red (TV coverage often uses magenta to distinguish it from the SPD)
Chairpeople: Katja Kipping, Bernd Riexinger
Parliamentary leaders: Sahra Wagenknecht, Dietmar Bartsch
2017 Bundestag election result: 9.2 percent (69/709 seats)
Voters: The Left party's stronghold remains the "new German states" in the former East, where its voters tend to be former communists who supported the German Democratic Republic (GDR), and protest voters who want to express their disenchantment with traditional parties. If polls are to be believed, many of these have switched to the populist nationalism of the AfD in the past two years.
History: Though it was only founded in 2007, the Left party has a much longer history, and is still considered a direct descendant of the Socialist Unity Party (SED) that ruled the East German GDR until reunification with the West in 1990.
The Left party was formed out of a merger of the SED successor, the Party of Democratic Socialism (PDS), and Labour and Social Justice - The Electoral Alternative (WASG), a west German movement of trade unionists and disgruntled SPD members alienated by the welfare cuts introduced by Gerhard Schröder. The most prominent of these defectors was Schröder's first finance minister and SPD chairman, Oskar Lafontaine, who later led the Left party and is still a prominent figure guiding the party from his Saarland base.
Partly because of its association with the East German dictatorship, the Left remains a pariah for the other mainstream parties, and has never been part of a federal government coalition - though it has some government experience at state level.
Platform: The Left is the only major German party that rejects military missions abroad. It also wants NATO to be dissolved and the minimum wage to be raised from the current rate of 8.84 euros to 12 euros ($14.10). Some political scientists still see the Left as a radical party that ultimately seeks to overturn the capitalist economic order, but the party itself actually only advocates stronger market regulation, stronger rental caps, and more social investment.
Preferred coalition partners: SPD, Greens
The Green Party (Bündnis 90/Die Grünen)
Chairpeople: Cem Özdemir, Simone Peter
Parliamentary leaders: Katrin Göring-Eckardt, Anton Hofreiter
2017 Bundestag election result: 8.9 percent (67/709 seats)
Voters: The Greens rely heavily on the well-educated, urban demographic for their voter base - and its strongholds tend to be major cities in western Germany, especially where universities are located. However, the party's voters have also aged significantly over its 30-year history: fewer than 10 percent of Green voters are now under 35. By the same token, Green voters have become more affluent over the years, and the Greens struggle to attract voters from lower income classes.
History: The Green party is probably the most successful counter-culture movement in Germany's post-war political history. The party, whose official name is Alliance '90/The Greens, grew out of an assortment of social protest movements of the 1980s that eventually unified.
Their supporters marched for everything from ending nuclear power to gay rights - while maintaining the key plank of environmental protection. Their success lies in the fact that all of these causes have been incorporated into mainstream politics since the alliance was officially founded in 1993 (the Green party itself was founded in 1980).
The party became truly prominent in German politics in the early 2000s, when it became junior coalition partner to Gerhard Schröder's SPD, and supplied his government with Foreign Minister Joschka Fischer. Still, its biggest electoral success came in 2009, when it claimed over 10 percent of the national vote for the first and only time.
Platform: Political pundits tend to divide the Greens between the "Realos" and the "Fundis" - the "realists," who are willing to compromise party aims to have a say in government, and the more left-wing "fundamentalists," who are closer to the party's counter-culture roots.
The Realos have slowly taken control of the party, to the extent that it is now leading a coalition with the conservative CDU in the southwestern state of Baden-Württemberg. While environmentalism remains a core cause (agriculture reform was a key Green achievement in the early 2000s), it has also tried to a push a leftist agenda on tax and social policy. However, the prospect of a coalition with the CDU suggests that it may opt for a more centrist approach during this legislative period.
Preferred coalition partner: SPD
Alternative for Germany (AfD)
Color: Light blue
Chairperson: Jörg Meuthen
Parliamentary leaders: Alexander Gauland, Alice Weidel
Voters: The AfD has poached voters from all the other major parties except the Greens, and has simultaneously succeeded in mobilizing many non-voters. The AfD scores best among middle income earners - though that is by no means its exclusive voter base, and draws voters from across social classes. Its membership, meanwhile, has one significant feature - only 15 percent are women.
2017 Bundestag election result: 12.6 percent (92/709 seats - 2 MPs have left the party since the election, and will be independent)
History: The right-wing nationalist Alternative for Germany (AfD) has surged to prominence in the four years of its existence. Founded just five months before the 2013 election as a euroskeptic party, the AfD very nearly entered the Bundestag. Since then, Germans have elected the AfD to every state parliament in regional elections as well as the European parliament.
The AfD was originally created by a group of neo-liberal academics as a protest against the single European currency. They were angered specifically by Merkel's decision to bail out Greece in 2010 following Europe's financial crisis. But a power struggle in 2015 ended with the ouster of party leader Bernd Lucke, who was replaced by Frauke Petry.
Petry, along with other prominent figures, set a much more overtly nationalist, anti-immigrant, anti-Islam agenda, a policy that scored some success during the refugee crisis of 2015. But Petry has now also left the party, seemingly in protest at the far-right extremist turn the party took in the run-up to the 2017 election.
In 2016, the AfD was the only major German party to welcome the election of US President Donald Trump and Britain's decision to leave the EU.
Platform: The AfD wants to seal the EU's borders, institute rigorous identity checks along Germany's borders and set up holding camps abroad to prevent migrants from heading to Germany at all. The party wants to immediately deport anyone whose application for political asylum is rejected and to encourage foreigners to return to their home countries.
The party insists on the primacy of "traditional" German culture and rejects Islam as a part of German society. It also questions the notion that climate change is man-made and wants to reverse Germany's ongoing transition to renewable energy sources.
Preferred coalition partners: Ruled out by all other parties, but closest in policy to the CSU.
Free Democratic Party (FDP)
Chairperson: Christian Lindner
Parliamentary leader: Christian Lindner
2017 Bundestag election result: 10.7 percent (80/709 seats)
Voters: As the party of neo-liberal free enterprise, it's no surprise that the FDP has found the most voters among the self-employed - especially business owners and professionals like dentists and lawyers - and the fewest among workers.
History: The Free Democrats were a permanent fixture in the German parliament from the early days of the Federal Republic. However, the party suffered major election losses in 2013, failing to clear the 5-percent hurdle to enter the lower house. It has struggled for relevance ever since, but then experienced a resurgence under new leader Christian Lindner, and is now re-entering parliament with some 80 Bundestag members and is likely to re-join the government in coalition with the CDU.
Founded in December 1948, the FDP has been kingmaker to both the CDU and the SPD in its time. Though it has never led a German government, it participated in government for a total of 41 years, longer than any other party. Consequently, it has provided the bigger parties with many cabinet ministers, some of whom, such as Helmut Kohl's long-term foreign minister, Hans-Dietrich Genscher, became major post-war historical figures.
Platform: The FDP's program is founded on the principles of individual freedom and civil rights. While it has always campaigned for more tax cuts, it opposes leaving the financial markets unbridled. It is also a pro-European party.
Preferred coalition partner: CDU