If federal arrangements are to adequately serve governing, they should promote both inclusion and differences. The degree to which federalism serves these aims by different institutional responses and strategies for achieving this tall order are analyzed for twelve countries in this volume. It is the seventh in a series of practical volumes on, “A Global Dialogue on Federalism,” that links academics and public officials. The Moreno and Colino volume examines how diversities are distributed, activated, politicized, and dealt with, and under what conditions different types of federal arrangements serve to accommodate social and political differences, manage conflicts, and stabilize legitimate orders. Following a common template, Diversity and Unity compares constitutional principles, socioeconomic differences, cultural-identity diversities, political differences, institutional arrangements, and policies for managing diversity. Each country faces somewhat different challenges. Generally speaking, Australia has no strongly pronounced ethno-cultural cleavages that are defined territorially. In contrast, Belgium experiences three main cleavages: socioeconomic, philosophical-ideological, and linguistic. Although Brazil does experience some territorial differences, particularly north–south, the federal challenges are more related to problems of access to economic resources, public policies, and citizenship. Canada not only has language but also regional differences, and issues of territorial minorities. Ethiopia is home to more than eighty “nations, nationalities and peoples.” In Germany, an otherwise homogenous country, the challenges of labor migration from other countries and unifying the former eastern Länder nevertheless present challenges. India, of course, faces multiple identities related to geography, language, religion, socioeconomic status, some of which threaten its unity as a nation state. The same concerns exist for Nigeria. However, only territorially has it recognized diversity. Finally, Spain’s internal diversity is highly territorial, manifested in various forms of historical interpretations and identity politics.