Who are they?
Die Linke formed in 2007 to represent German socialist voters, since many on the far left felt that their values had been betrayed by the Social Democrat (SPD) chancellor Gerhard Schröder, whose Agenda 2010 economic plan - which included large cuts to unemployment and pension benefits - was seen as an attack on the working class.
The party was created from a merger of several smaller socialist and social democratic parties including the Party of Democratic Socialism - the successor to East Germany's communist party, the SED.
Die Linke describe themselves as the party of democratic socialism, standing for left-wing economic values, but also campaign against fascism and prejudice.
They claim fighting the rise of far-right populist parties such as the NPD (Nationalist Party of Germany) among their main objectives.
Who's their leader?
Gregor Gysi, 65, grew up in Treptow, a small district in what was then communist East Berlin. Whilst studying law at Berlin's Humboldt University, he joined the SED (the ruling communist party in East Germany).
After graduation, Gysi qualified as a barrister in 1971 and went on to defend several outspoken critics of the communist government. After gaining his law doctorate in 1976, he was appointed chairman of the Berlin college of lawyers.
Gysi spoke at demonstrations in Alexanderplatz, East Berlin, on November 4th 1989 arguing for the right to vote and a constitutional court.
During the period of Germany's reunification, Gysi served as chairman of the SED, which in 1990 reformed into the PDS.
Gysi was leader and chancellorship candidate for the PDS in 2005, a role he continues to serve since the party merged with others to form Die Linke.
His legal career has stood him in good stead for political leadership. He is renowned for his public speaking skills, and has been hailed as one of Germany's best rhetoricians.
What's their strategy?
Die Linke are campaigning on a ticket comprising traditional left-wing economic policies. The party favours expansive government regulation of the market economy and major tax increases for the wealthiest citizens, as well as a 'robin hood' type tax on large financial transactions.
They argue for the abolition or strict regulation of private healthcare to create a fully socialized system in which every citizen has the same entitlement to care, however rich or poor.
They also support the introduction of a minimum wage, and have extensive plans to improve working conditions and benefits, including increasing the minimum state pension.
Their campaign is built around the message that the same economic policies which made Germany one of the richest countries in the world have kept many of its people desperately poor and deepened divisions in German society.
Why do they matter?
Die Linke have often been seen as an unrealistic political option, a fringe party that would not get near real political power.
Both the SPD and Greens have stated outright that they would not form a red-red-green coalition with Die Linke, whom they see as too extreme-left.
However, the potential importance of Die Linke in post-election coalition talks became more prominent last week, when the latest opinion poll figures showed them up two points at ten percent, one point above the struggling Greens.
Die Linke have traditionally rejected the possibility of entering a coalition with either the SPD or the Greens, neither of whom they believe represent the interests of the working class.
But Bernd Riexinger, co-chairman of the party, recently told the Berliner Zeitung that his party would "not rule out" tolerating a red-green minority government in the event that the CDU doesn't gain an absolute majority, suggesting they would agree to vote along with a potential SPD-Green government in order to keep Merkel's Christian democrats out of power.
The Christian Democratic Party (CDU)