This chapter provides some essential contextual information on the Labour Party, the Parti Socialiste, the Sozialdemokratische Partei Deutschland, and the Party of European Socialists’ organisations. The chapter first summarises each party’s historical background. Second, it describes the three different faces of each party organisation (on the ground, in public, and in central office). It argues that amongst the three parties, Labour has become the most ‘centralised’, as the leadership at Westminster has assumed much power in the formulating policy. The PS is also a highly centralised party, as the most important decisions are taken by a small circle of leaders in Paris. At the same time, the PS continues to be dominated by rival factions that form around potential presidential candidates. The SPD, by contrast, is a more decentralised party in which power is shared by the regional associations and the national party federation. Thus, the three parties - whilst being centre-left, multi-level, and multi-faceted parties of government - organise very differently. Still, there are challenges that the parties share, such as the lack of grassroots engagement and the rise of rival left-wing social movements.