The vast majority of political parties can be categorised into a handful of party families, such as liberals, conservatives, social democrats and greens. Parties within the same family share a common ideological heritage, occupy similar positions within their respective party systems (with social democrats typically on the left, liberals in the middle, and conservatives on the right), and tend to align on a wide range of issues. They also seek proximity to one another, often forming party groups in institutions such as the European Parliament.

While most parties maintain fidelity to their ideological legacy, shifts do occur, as seen when former communist parties across Western and Eastern Europe rebranded themselves as democratic socialists following the end of the Cold War.

The continuity of ideology is significant to voters, as various explanatory models of voter behaviour suggest. While economic, social, and individual factors all play a role, studies consistently indicate that voters generally align closely with the ideology of the parties they support. Therefore, for voters, knowing that a party is “socialist,” “green,” or “liberal” is crucial in informing their choices on election day.

In what follows, we discuss the relevant aspects of the changes in European politics over the past seventy years. While unique circumstances may explain individual election results for specific parties in particular countries, there are likely common circumstances underlying long-term trends for entire party families.