During much of the 20th century, the national party systems of Western Europe remained largely unchanged. However, beginning in the 1970s, these frozen party systems slowly started to melt. As the number of parties has increased, the question of what explains new party entrance has also attracted more scholarly interest. Despite this increased attention, the study of new political parties still suffers from a structuralist bias. The implication is that the fates of new parties are decided almost exclusively by external factors. Some scholars focus on the institutional environment; others emphasize sociological explanations, such as the formation of new cleavages in society. Yet such non-actor-centred perspectives risk being excessively deterministic. They also struggle to explain why some parties succeed in gaining entrance to legislatures while others, seemingly under the same external circumstances, fail. In this thesis, therefore, a new way to study parties and their path to parliament is proposed. Starting with the notion that external conditions alone cannot explain new party entrance, the thesis takes an agency-based perspective. Three sets of strategies are identified as being important means for a party to influence its chances of getting into parliament. They concern the party's resources, its political project and its external relations. In what ways can supply and management of resources, policies and relations with other parties affect the potential for becoming a parliamentary party? Through four in-depth case studies of new entrants into the Swedish national parliament, the Riksdag, the thesis concludes that there are some important commonalities in their paths to parliament. Especially with regard to their resources and their political project, the empirical evidence supports the initial premise: new party entrance is unthinkable without successful strategic behaviour.

During much of the 20th century, the national party systems of Western Europe remained largely unchanged. However, beginning in the 1970s, these frozen party systems slowly started to melt. As the number of parties has increased, the question of what explains new party entrance has also attracted more scholarly interest. Despite this increased attention, the study of new political parties still suffers from a structuralist bias. The implication is that the fates of new parties are decided almost exclusively by external factors. Some scholars focus on the institutional environment; others emphasize sociological explanations, such as the formation of new cleavages in society. Yet such non-actor-centred perspectives risk being excessively deterministic. They also struggle to explain why some parties succeed in gaining entrance to legislatures while others, seemingly under the same external circumstances, fail. In this thesis, therefore, a new way to study parties and their path to parliament is proposed. Starting with the notion that external conditions alone cannot explain new party entrance, the thesis takes an agency-based perspective. Three sets of strategies are identified as being important means for a party to influence its chances of getting into parliament. They concern the party's resources, its political project and its external relations. In what ways can supply and management of resources, policies and relations with other parties affect the potential for becoming a parliamentary party? Through four in-depth case studies of new entrants into the Swedish national parliament, the Riksdag, the thesis concludes that there are some important commonalities in their paths to parliament. Especially with regard to their resources and their political project, the empirical evidence supports the initial premise: new party entrance is unthinkable without successful strategic behaviour.