This chapter explains the book’s origins. Visits to Chicago’s Mexican churches suggested a complex, multiethnic history that required learning about Chicago’s eastern European immigrants. Mexican immigrants and their children shared memories of the communities they encountered, reshaped, and made anew in Chicago. The ability to carry out Catholic devotions and to join parishes proved essential for most Mexicans and the communities that they built in the United States. The chapter considers relevant scholarship in Latino studies, which lacks attention to religion. US Catholic history, meanwhile, sorely needs more work on Latino communities and religious life. This book underlines religion’s critical role in urban adjustment and racial politics while recasting the Eurocentric assumptions of immigration history narratives.