Sweden can be seen as a testing ground for a new form of coalition government called ‘contract parliamentarism’. Tim Bale and Torbjörn Bergman (2006a: p. 422) define contract parliamentarism as follows: ‘in contract parliamentarism, what are formally minority governments (formed by either a single party or a coalition of parties) have relationships with their “support” parties that are so institutionalised that they come close to being majority governments.’ Next to the Swedish Greens (Miljöpartiet den Gröna, MP), the Swedish Left Party (Vänsterpartiet, V) was the main support party of Social Democratic governments between 1998 and 2006. As we shall see in the following, the Left Party, after achieving an all-time electoral high of 12 per cent in 1998, suffered badly at the polls during this period and, indeed, afterwards. Even though Bale and Bergman (2006a, b) analysed contract parliamentarism closely, they paid scant attention to the Left Party. This chapter aims to fill this gap and addresses three major questions: first, why did V end up as a support party rather than a coalition partner? Second, which factors caused the collapse of the Left Party’s electoral appeal after 1998? Third, how much did this collapse have to do with V’s role as a support party? In order to answer these questions, this chapter proceeds as follows. After first discussing V’s background as a Communist party, I provide an overview of the (institutional) context of the Swedish party system. Then I trace V’s ideological development before, during and after its experience as a support party. The next section discusses the consequences of V’s support party experience, while the final section provides a brief analysis of the party’s future prospects. As we shall see, a combination of unfavourable institutional factors and unsolved strategic dilemmas weakened V’s bargaining power vis-à-vis its support partner (the Social Democrats). More ominously, on account of the structural changes within the Swedish party system the future prospects of V joining a coalition government are anything but rosy.