This chapter introduces the Texas-California sibling rivalry. All states can be considered “siblings,” but the connections between Texas and California are especially strong. The ties include common origins as territories of Spain and Mexico, Sun Belt geography, rich natural resources, vibrant economies, large-scale immigration, and comparable demographics. Moreover, in the past, Texas and California agreed on a range of political questions. In the 1990s, however, the two states began to divide. In the years since, they have hardened their partisan identities and come to advocate more sharply opposing visions of government. More than other states, California and Texas have driven our contemporary national polarization. The chapter presents the book’s central questions: Why, despite their similarities, have Texas and California divided? How have these states translated their competing visions into policy? And what does the future hold for these models—both for these two states and for the nation as a whole?