IntroductionThis paper explores the dynamics of regional party systems in a comparative analysis of three 'small worlds' in Canada and Europe. The analysis forms part of wider exploration of the enduring impact of Elkins and Simeon's (1980) book Small Worlds on approaches to political science. The paper draws primarily on Elkins' analysis of Canadian provincial party systems. His research revealed that there was a strong regional dimension to party competition and that 'parties were themselves divided along provincial lines as much as party lines'. Elkins recommended two paths of further research: greater in-depth analysis of regional systems, and a broader comparison across countries. This paper aims to meet both these requests.Québec, Bavaria and Scotland are three regions nested within multi-level states. Each has a pronounced territorial identity and a strong regionalist party, factors that have contributed to an important territorial cleavage in political life. These cases have also been described as 'stateless nations' embedded in the larger structure of the state, presenting alternate worlds for political socialisation. As individual 'containers' of social attitudes and behaviour, these small worlds have distinctive party systems reflecting the efforts of regional parties to reflect the values of the electorate. The aim of this paper is to unpack territorial differentiation in Québec, Bavaria and Scotland by exploring the internal dynamics of party systems, and their integration into the state. It also modestly aspires to extend parts of Elkins and Simeon's thesis by introducing new research on party competition through the lens of multi-level politics, and by translating the Small Worlds thesis to a European context. The paper begins with a review of recent European approaches to party behaviour in multi-level systems, before introducing the rich body of literature in Canadian political science exploring the organisation of parties along federal-provincial lines. In particular, it considers the methodological relevance of Elkins and Simeon's Small Worlds thesis for the analysis of regional politics beyond Canada. Three lines of questioning about regional party systems, which were originally posed by the authors in 1980, are then discussed in the context of present-day developments in Canadian and European territorial politics. Specifically, these questions deal with: (1) the (in)congruence of party systems and competition at the regional and state levels; (2) the adaptation of statewide parties to the regional level; and (3) the conduct of party competition on regional issues. These three indicators of distinctive political 'small worlds' are then explored in detail in each of the case studies. The final part of the paper compares party competition in multi-level political settings, and considers the continuing relevance of the Small Worlds thesis for the analysis of regional party politics in newly decentralising as well as established federal states in Canada, Europe and beyond.