Book excerpt: "Over the past three decades, there has been a global sea-change in the nature of international migration. In myriad places around the world this kind of deep shift has had significant impacts on the local configurations and dynamics of diversity. Old and new immigration sites across the world have experienced rapid and increasing movements of people from more varied national, ethnic, linguistic and religious backgrounds. These movements have emerged along with a diversification of migration channels and legal statuses and, more broadly, greater societal attention towards identity politics Worldwide, in concurrent but differing ways, these migration-driven trends are deeply transforming societies in complex ways spanning social, demographic, cultural, economic and political structures. Now across a range of disciplines and literatures, such complex transformation processes and patterns are summarized by the concept of superdiversity (Vertovec 2007). As the world emerged from the end of the Cold War and the collapse of the Soviet Union, we saw Western democracies promoting the universalisation of liberal democracy and its values (Fukuyama 1992). The consolidation of the international human rights regime, with human rights becoming the 'lingua franca of global moral thought' (Ignatieff 2001: 53), was part of this process (Douzinas 2007). That move provided the ideological scaffolding for neoliberal economic globalisation which relied on enhanced international circulation and interdependence of capitals, goods, services, and supply chains. With goods and services, also human mobility grew, and with increased material and more recently digital connectivity, new destinations and routes became appealing, available, and affordable (IOM 2021). Meanwhile, the 'end of history' and the consolidation of the post-Cold War geopolitical order didn't come peacefully and triggered a series of regional and international conflicts that in turn led to a growth of international and internal displacement globally, a trend that is now increasingly fuelled by climate change and environment degradation acting as key factor in migration dynamics (Black et al 2011). International migration is both an effect and a driver of these developments. It crucially contributes to establish and consolidate transnational networks and diasporic communities, while at the same time it is a key contributor to the diversification of host societies. In myriad settings around the world, there are people with more varied ethnic, racial, linguistic, religious, and legal status characteristics than ever before - each set of characteristics intersecting differently with others as well as with age, gender, and class. As a result, "the world is much more diverse on multiple dimensions and at many levels, typified by the salience of differences and their dynamic intersections" (Jones and Dovidio 2018: 45). Contemporary immigration societies have become increasingly diverse, layered, and unequal. Indeed, 'the processes of neoliberal globalization have gradually loosened labour protections, restructured the welfare system, delocalized state borders, and led to widening inequalities' (Gonzales and Sigona 2017: 3), putting pressure on the connection between state, territory and residents, transforming traditional notions of sovereignty and citizenship, while also giving rise to a host of new non-state actors operating transnationally (Sassen 2006; Castles 2001). As evidenced by its ubiquity across the social sciences, superdiversity is one of the most prominent contemporary concepts advancing current understanding of international migration and its social implications. The numerous social scientific debates, approaches and methodologies that have been developed in light of superdiversity speak to each other but have not yet been brought together in a single volume. This handbook fills this gap in the literature, offering students, educators, researchers and practitioners a much sought-after compendium of central advances made in studying complex social transformations in light of superdiversity. The chapters take stock of some of the advances in the field and lay out the importance of engaging with complex social transformations in light of migration-driven change. In this introduction we frame the discussions that follow by first elaborating the notion of complex social transformations and its resulting complexities, then providing an overview of how we structured the book and the types of chapters you will find in the different sections of this handbook. "--