Policy diffusion has become one of the most vibrant areas of research in the study of American state politics, and State Politics & Policy Quarterly (SPPQ) has played a leading role in shaping that scholarship. While scholars agree that states routinely look to one another when making policy decisions, questions persist about the mechanisms that drive these processes, the methods best suited to studying them, and the implications for policymaking. This article reviews 25 years of diffusion research published in SPPQ. We classify articles into four categories – those developing theory, advancing methods, applying diffusion insights to substantive policy domains, and diffusion-adjacent studies – and analyze both their content and contributions. Our review highlights the richness of this work, the frequent overlap across categories, and the distinctive advantages of studying diffusion in state politics. We conclude by outlining opportunities for the next generation of research and reaffirming SPPQ’s role in advancing the field.

Drawing on the theory of policy diffusion, I analyze 129 regulatory firearm law provisions from 1991 to 2019 across the United States and examine the innovation and development of restrictive firearm policies. I control for the demographics, politics, and institutional characteristics of the states and hypothesize that public health concerns lead to the adoption of firearm regulations. I find support for my hypothesis: most novel, state firearm policy diffusion is dependent on state firearm suicide and homicide rates. Furthermore, I find that states are more likely to adopt policy if they are characterized by a large population, a large white population, high firearm ownership, a liberal government, or if their geographical neighbors are actively adopting firearm regulations. Firearm-related fatalities have risen dramatically, but a majority of states have adopted few policies to address this public health concern. My article highlights the state-level factors that produce a public policy response to this phenomenon.

Most quantitative analyses of policy convergence treat transnational communication in international organisations and domestic economic problems as additive factors. By contrast, this article argues that domestic economic problems motivate governments to search for successful policies, while international organisations offer channels for policy learning. Thus, both factors interact, magnifying each other's effects. The argument is corroborated by a quantitative analysis of the privatisation of telecommunications providers in the Western OECD world. A dyadic logit model shows that joint membership in international organisations increases the likelihood of policy convergence if governments face budget deficits. The argument of the article builds a bridge between theories of international organisations and domestic theories of policy making. Theories of the former gain an important scope condition specifying the conditions under which transnational communication works, while exploring the latter gains a theory specifying where new policy ideas come from.

This article discusses the recent literature on policy diffusion and puts forward a new articulation of its political dimensions. Policy diffusion means that policies in one unit (country, state, city, etc.) are influenced by the policies of other units. The diffusion literature conceptualises these interdependencies with four mechanisms: learning, competition, coercion and emulation. The article identifies a model of diffusion that is dominant in the diffusion literature. According to this model, policies spread because decision makers evaluate the policy implications of the actions of other units. It is argued that the role of politics remains in the background in this model, and the article shows how going beyond a narrow focus on policy adoptions helps us to consider the politics of policy diffusion more explicitly.

Although it is widely accepted that a decentralised system can enhance policy learning and the spread of best practices, an under‐researched question is where that learning process takes place. Using data on the diffusion of health care policies in Switzerland, this article analyses the role of institutionalised intergovernmental cooperation and its impact on the spread of successful policies. The results show that joint membership of policy makers in health policy specific intergovernmental bodies is related to the diffusion of best practices.

Event history analysis (EHA) revolutionized the study of policy diffusion. However, many diffusion studies are snapshots of a policy’s spread. This begs the question of what we are learning from studies of (often) incomplete diffusion. The simple question that we ask – when should a diffusion study be conducted? – is complex to answer. We offer insight into this question using literature on EHA and empirical observation. We use data from the State Innovation and Policy Diffusion database on 83 policies that were adopted by at least 42 states to demonstrate how key results change as the observation window changes. We conclude with advice on how to approach modeling and interpreting incomplete policy diffusion in the future.

Between 1980 and 2020, more than 120 countries—Canada included—enfranchised emigrants. While the diffusion of democratic practices is a well-established international phenomenon, we know little about the domestic process. How does international policy diffusion influence domestic debate? To explain the structure of Canadian debate about emigrant voting rights, we draw on concepts from the constructivist literature on international norms. In examining the structure of normative discourse within a domestic context, we argue that emulation involves three rhetorical elements that can generate disagreement: (1) setting peer countries to emulate; (2) identifying existing policy positions; and (3) envisioning the preferred policy position vis-à-vis peers. We find that in the Canadian debate about emigrant voting, contestation increased over time; where only peer groups were contested in the early debates leading up to the initial 1993 enfranchisement, all three elements were contested when discussing the removal of temporal restrictions two decades later.

The suboptimal size of municipalities is often a challenge for service delivery due to scale limitations. Intermunicipal cooperation (IMC) has expanded as an alternative to top-down amalgamations, offering a more flexible and typically voluntary approach. Many studies have been devoted to understanding the driving factors of IMC, providing static empirical evidence on the characteristics of cooperating municipalities. This article contributes to the literature with a dynamic analysis of the drivers of cooperation, using a Cox proportional hazards model over a long period and a very large sample of municipalities in Catalonia. This dynamic analysis unravels the direction of the causal relationship in complex relationships such as fiscal restrictions or political legitimation with cooperation. Furthermore, as we have data from eight relevant local services, we improve both the theoretical and empirical analysis of cooperation dynamics based on the characteristics of the services.

Many countries globally have adopted national policy commitments to address violence against women (VAW). Yet the implementation of these policies largely relies on subnational governments’ actions. Why do some but not all subnational governments adopt policies to implement VAW response services? Surprisingly, few studies have addressed this question. Drawing on norm diffusion and gender policy reform theories, we assess the factors driving the adoption of these local policies in Indonesia. Since Indonesia adopted its domestic violence law in 2004, only one-third of cities/regencies have adopted local regulations (peraturan daerah) on VAW response services. Using event history analysis, we analyzed data from 509 cities/regencies from 2004 to 2022. Our findings show that the presence of local non-governmental organizations (NGOs) connected to national and transnational VAW advocacy networks, and women’s local legislative representation are significant factors. However, province-level morality regulations constrain the progressive effects of the VAW advocacy networks and women’s political presence.

While existing research on policy diffusion has provided substantial evidence regarding the drivers of policy adoption across jurisdictions, limited attention has been given to the dynamics of policy textual learning across different levels of government. We fill this gap by using regression analysis to examine the patterns of policy textual learning evident in the clause similarity of seven environmental statutory policies in China. Within China’s decentralized and multilevel environmental governance, our findings reveal that horizontal policy textual learning is more prominent than vertical learning. Temporal distance negatively impacts policy textual learning, whereas spatial distance, contrary to traditional policy diffusion perspectives, does not universally explain multilevel policy textual learning. Additionally, subsequent versions of policy texts are not necessarily similar to earlier ones, challenging conventional assumptions about the adoption and adaptation of policies over time.

The development of father leave policies marks a critical step toward gender equality in family policy. Despite promising policy developments, father leave policies continue to face resistance and negative feedback from various stakeholders, constraining their development. Their implementation has exhibited considerable variation across countries, ranging from mere symbolic gestures to substantive reforms. This article provides a comprehensive framework for understanding their evolution, emphasising that progress depends not solely on public support but on a mix of factors, including electoral competition, policy diffusion, negative feedback, and crises. The contrasting outcomes observed in South Korea and the Czech Republic highlight how similar drivers can produce divergent policy responses, challenging the view that drivers (like crises or electoral competition) have a predictable effect on policy change. This complexity necessitates a re-evaluation of existing theoretical frameworks to more accurately reflect the intricate dynamics at play in policy development.

This article proposes a theoretical framework for explaining the motivations behind the early adoption of international public policy innovations. While there has been a proliferation of transnational policy diffusion studies, there is less research on why some governments become early adopters when new international policy norms are promoted. Most research on the topic looks only at monocausal explanations without considering their interactions in a coherent, integrated framework. The article proposes four motivations for early adoption: normative, reputation, competition, and locking-in. The framework is then illustrated by application to the early adoption of business and human rights policy innovations, with Colombia and Ecuador serving as two cases for comparative analysis. The article advances understanding of early adoption and policy diffusion by highlighting particularly important explanations for what motivates early adopters to begin processes of subsequent diffusion and suggesting how motivations may interact to strengthen the case for early adoption.