LIKE MUCH OF Germany's democratic machinery, its voting system is designed to avoid past mistakes. A combination of proportional representation and first-past-the-post majority voting fosters stable coalitions and discourages small fringe parties. When Germans go to the polls on September 22nd, they will elect the members of the Bundestag, or lower house of Parliament. Whichever coalition of parties can muster a majority of members will form the federal government. Members of the Bundesrat, the upper chamber, are delegates of Germany's 16 states, or Länder. Germans have two votes. One is for a candidate to represent the local electoral district (of which there are 299), chosen by simple plurality of votes. The second vote is for a party. Any party receiving 5% or more of the total is entitled to seats in the Bundestag, whether any of its candidates have won a district or not. If a party gets more seats through direct election than its share of the overall vote merits, it can keep some of these "overhang" seats. Thanks to a recent change in the electoral law, the other parties then get "compensatory" seats to restore the balance among the parties. These provisions mean the precise number of Bundestag members will not be known until after the election, but it could reach 700. Germany's biggest party is the ruling conservative Christian Democratic Union (CDU), led by Angela Merkel, together with its sister party in Bavaria, the Christian Social Union (CSU). The overall group is known as the CDU/CSU. The group's support has risen in recent years and is currently around 40% in opinion polls (see chart 1). The second-biggest is the centre-left Social Democratic Party (SPD), support for which has fallen in recent years and is now about 27%. Its candidate for chancellor is Peer Steinbrück. Neither of these two parties is big enough to win a majority of seats in the Bundestag on its own. In the past one or the other of them has formed a coalition with one or more of the smaller parties, or with the other big one. The CDU/CSU currently governs in coalition with the liberal, free-market Free Democratic Party (FDP), but support for that has been slipping and it might not reach the 5% needed to be represented in the lower house. The fourth party in the Bundestag is Die Linke ("The Left"), formed from the rump of East Germany's communist party and joined by defectors from the SPD. In Germany's most recent federal election in 2009 Die Linke got 12% of the vote. The SPD has ruled it out as a coalition partner. Germany's fifth party, in terms of seats in the current Bundestag, are the Greens. They started life as an environmental party in the early 1980s and now form part of coalition governments in several of Germany's Länder. Polls suggest they could win about 14% of the vote. Two other small parties have been formed in recent years. The Piraten ("Pirates"), dedicated to internet freedom, caused a splash when it first appeared in 2006, but has lost momentum and now gets only about 3% in polls. The newest start-up is Alternative für Deutschland ("Alternative for Germany," AfD), a Eurosceptic party formed in April this year. The latest opinion polls give it 3% of the vote, but it is gaining ground and could reach the 5% threshold. Since its support seems to be drawn mainly from CDU and FDP voters, that would make a victory for the left more likely. All this leaves the post-election political line-up uncertain. If the FDP performs well enough, the chances are that Mrs Merkel will continue in government with the present "Black-Yellow" coalition of the CDU/CSU with the FDP. If both current coalition partners do poorly, Mr Steinbrück may try to put together a centre-left "Red-Green" grouping of his SPD with the Greens. If there is insufficient support for that too, the two big parties may join in a "Black-Red" grand coalition, as they did in Mrs Merkel's first term of office. This is widely seen as the most likely outcome. Last time the voters did not seem keen on it, punishing the SPD in the subsequent election. But this time the polls suggest some enthusiasm for the idea.