This an ambitious and impressive book written around the concept of party system closure. The study of party systems as systems with their own internal dynamics and logics is a classical subdiscipline of political science, going back to Giovanni Sartori and prominently continued by Peter Mair. However, it is also a research strand that has been declining in terms of political scientists’ attention. This is paradoxical because there is still enormous interest in political parties. The literature on the many new political parties emerging in West European party systems is extensive. Yet today, political parties are rarely studied from a party system perspective.

Having read this excellent book by Fernando Casal Bértoa and Zsolt Enyedi, it is clear that this limited attention to the party system perspective is a major omission on the part of the discipline. The book makes a persuasive argument for why studying the institutionalization of party systems provides a long-term and comparative perspective on political parties that contains highly important new insights. For instance, it shows that, although West European parties have clearly changed, the change is much less dramatic when viewed from the party system perspective, rather than using concepts like polarization and fragmentation, which are much more fashionable in political science today.

The major contribution of the book is its development and application of the concept of party system closure. This concept was originally developed by Peter Mair to explain the phenomenon of party system development: it captures the patterns of interactions among political parties, rather than just political parties’ individual attributes, like vote share. The central idea underlying this concept is that the key interaction of political parties occurs around government formation. Thus, a closed-party system is one where government alternatives are familiar and predictable.

Closure is understood as having three dimensions. The first dimension is alternation, which describes whether a change of government is complete or only partial. A system with only complete changes of governing parties is considered closed because the government alternatives are clear. When changes in governing parties are only partial, the government alternatives appear less clear. The second dimension is familiarity. Are the government alternatives stable and well known? The third dimension is access. Do new parties have easy access to government power? The concept of closure thus describes whether party relation with regard to government coalition building is structured around a few clearly defined and stable groups of parties that enter and leave office together. Party system closure is seen as a central aspect of the broader concept of party system institutionalization, which refers to the stability and predictability of party interaction more broadly; that is, not just in terms of government coalition formation.

The book is structured around party system closure. Chapter 2 presents the impressive dataset from which the authors draw and shows how the different dimensions of the concept can be measured. The dataset covers all democratic European states from 1848 to 2019. The time span is thus wide, and so is the geographical span from the Atlantic to the Urals, including small states like Andorra and San Marino. Because of the long time period covered, some countries have had several party systems. Altogether, the dataset consists of an impressive 65 party systems.

The rest of the book analyses this dataset in multiple ways. Chapters 3–5 use the concept of party system closure to analyze party system development in both existing and defunct party systems. Chapters 6–9 analyze how party system closure covaries with different factors like the age of the party system, the age of the parties within a given system, the number of parties (party system fragmentation), and how polarized those parties are, understood as the strength of anti-establishment parties. In chapter 10, these four factors are put together in an explanatory model. In chapter 11, party system closure is then used as an explanatory variable to predict democratic survival, which to some extent it does.

For anyone interested in party system development, the book is a great and very informative read. It fully convinced me that looking at party systems through the lens of party system closure is crucial for our understanding of their development. The focus on the stability and predictability of party interactions around government formation is an important one that gives a quite different perspective than an approach based on fragmentation and polarization. That being said, the book is sometimes a bit challenging to digest. The dataset offers a great many possibilities for analyses, but perhaps not quite so many should have been explored in so much detail within one book. The book is also very heavy on tables and figures, which sometimes may it difficult to keep sight of the main points. The long time period is in many ways a strength of the book, but it also raises questions about comparability over time. Party systems operate in a quite different context today compared to the second half of the nineteenth century, which perhaps affects their relationships. This question deserves more attention. The book is also more successful in its descriptive than its explanatory ambitions. How the various factors analyzed in chapters 6–9 relate to party system closure is interesting, but it is not always obvious what the causal direction is, and some readers might also find that the causal distance between the variables is not large. In general, the book pays very little attention to explanatory factors external to the party system.

Yet, none of these more critical comments should distract from the fact that Bértoa and Enyedi have written an important book that will, I hope, put party system analysis back at the center of the political science stage. European party systems are witnessing turbulent times, and the need for strong analytical concepts has never been greater. This book delivers exactly such concepts.