Winning Germany's most populous state - the last to vote before September's general election - could provide key momentum. And there are many other reasons why parties want a strong showing in North Rhine-Westphalia.
This Sunday, more than 1,300 candidates from 31 parties were being selected by the 13.2 million eligible voters in the state of North Rhine-Westphalia (NRW). For the past few weeks, Chancellor Angela Merkel's Christian Democrats (CDU) and their main rivals - and coalition partners at federal level - the center-left Social Democrats (SPD), have been furiously campaigning to win the state. Meanwhile, the right-wing Alternative for Germany (AfD) could enter the state parliament for the first time.
With nearly 18 million residents - about 20 percent of Germany's population - NRW is the most populous of the country's 16 states and also the biggest contributor to national gross domestic product - besting even the economic powerhouses Bavaria and Baden-Württemberg.
NRW is also the last state to vote before the federal general election on September 24. Being part of the ruling coalition in NRW also means having a significant say in federal legislation. The ruling coalition sends six representatives to the 69-seat Bundesrat, Germany's upper house of parliament, which proposes new federal laws and can block those passed by the nationally elected lower house of parliament, the Bundestag.
The current situation
NRW has been governed by a center-left coalition of the SPD and the Greens since 2010, with the Social Democrat Hannelore Kraft serving as state premier.
NRW's premier Hannelore Kraft (center right) is seen as one of the SPD's most important figures, along with Foreign Minister Sigmar Gabriel (left) and Martin Schulz, leader of the SPD (center)
The center-right CDU, the pro-business, liberal Free Democrats (FDP) and the left-wing Pirates have been the parliamentary opposition since the last election, in 2012.
NRW has long been an SPD stronghold. Residents of the industrial Ruhr region maintain a strong connection to the party, which was founded to represent workers' interests, as do many Germans with Turkish roots, a large community in the state.
Aside from the period from 2005 to 2010 when the CDU governed with the FDP, the SPD has been the top party in NRW's coalition since 1967.
With the CDU mounting a strong challenge to the SPD this year, even December's attack on a Christmas market in Berlin has become an issue in the state's elections. An immigration office in NRW had overseen the case of Anis Amri, a man from Tunisia who was killed by a police officer in Italy after allegedly carrying out the attack. Even though state officials had rejected Amri's asylum application and categorized him as a "person likely to threaten public safety," he was never arrested or deported. The FDP and Pirates have called for NRW Interior Minister Ralf Jäger, who oversees the state's immigration authorities, to step down. State premier Kraft has rebuffed criticism of Jäger.
Education is also playing a big role in NRW's elections, with candidates debating a new approach to the state's two-track public school system, which separates students early according to educators' assessments of whether they would be better off pursuing apprenticeships or academic paths. Another major issue is how students with disabilities should be integrated into schools that have been less accessible to them.
Traffic and infrastructure have also been hotly debated. The opposition has accused the SPD and the Greens of not doing enough to maintain the state's streets and to curb the infamous traffic jams that clog the extensive highway network.
What is the likely outcome?
Six parties could realistically make it past the 5 percent threshold required to qualify for the state parliament: the SPD, CDU, FDP, Greens, AfD and the Left (Die Linke). The Pirates are not expected to enter the parliament again.
Current polls show the SPD and CDU running a close race, with the Social Democrats only slightly ahead. According to a survey conducted for public broadcaster ZDF, both parties are polling at 32 percent. A survey for the Bild daily shows the SPD three points ahead of the conservatives at 33 percent. A win for either party would send a signal to voters and pundits ahead of September's national elections.
For the SPD, losing NRW to the CDU could be a fatal blow. After the party announced that Martin Schulz, the former president of the European Parliament, would be their candidate for chancellor, their numbers in national polls increased rapidly, but they have since fallen almost as dramatically. The SPD failed to capitalize on the "Schulz effect" in both the Saarland state election in March, where the CDU held on to the state house easily, and in the Schleswig Holstein state election last weekend.
Chancellor Angela Merkel (center left) visited NRW to campaign for the CDU and their top candidate, Armin Laschet (left)
Taking NRW could help the CDU regain its momentum - and assert its dominance - after the SPD enjoyed a modest temporary uptick in support in national polls. The CDU managed to score a massive victory when it bested the SPD in Schleswig-Holstein. Germany's most northern state will now likely become the first state the CDU recaptured since Merkel took office 12 years ago. Winning NRW could put them in nine of Germany's 16 state governments.
The potential kingmakers
The Greens - polling at just about seven percent in NRW and nationally - are trying to prove that they do not lack relevant policy proposals and distinction from other parties. While the party just scored an impressive 12.9 percent in Schleswig-Holstein last weekend, few believe that the Greens can come even close to their last NRW election's 11 percent score. Top candidate Sylvia Löhrmann has been highly embattled. As education minister, she oversaw, among other things, an effort to integrate disabled students into regular schools that - some teachers and parents alleged - overwhelmed understaffed schools.
Education Minister Sylvia Löhrmann is leading the campaign of the Greens in NRW - with mixed results so far at best
Founded in 2013, the AfD will be on the ballot in NRW for the first time. The party is expected to narrowly clear the 5 percent threshold. This would make NRW the 13th state whose parliament the party has entered since 2014. The AfD's top candidate in NRW, Marcus Pretzell, does not just represent his party in the EU parliament (where he is part of a group led by Marine Le Pen that is often labeled right-wing extremist). He is also married to and expecting a child with Frauke Petry, the party's embattled chairwoman. So a good performance in NRW is key for the party, which has recently fallen significantly in polls, both in NRW and nationally.
The Left party is hoping to re-enter the parliament after receiving just 2.5 percent of the vote in the last election. The party is currently polling at five to six percent. Their top candidate is Ozlem Alev Demirel, a Turkish-German politician from a Kurdish family.
The Left party, with top candidate Ozlem Alev Demirel (pictured at an anti-AfD protest in Cologne), is hoping to re-enter the NRW parliament
The FDP is expected to be the third-strongest party on Sunday. The most recent polls show the business-friendly liberals at 12 to 13 percent. In 2013, the party suffered a historic loss in the national election when it failed to meet the 5 percent threshold. After a strong showing in Schleswig-Holstein, the party is hoping to score big in NRW to re-establish themselves as a national political contender.
Christian Lindner (center) is hoping to score big for the liberal FDP in Germany's biggest state - and then move back to national politics
The party's chairman, Christian Lindner, is leading the campaign efforts in NRW, but he has also declared his candidacy for the Bundestag elections later this year.