This chapter develops the core theoretical framework, positing that patriotism functions as a psychological benefit in citizens’ cost–benefit calculations for collective action. When individuals perceive their country as offering freedoms and opportunities, they feel gratitude and a desire to “repay” those benefits through pro-social or civic acts. The chapter introduces formal models illustrating how a sense of mutual obligation—“I owe something to my country”—can spur volunteerism, voting, and other participatory behaviors, and it addresses concerns about whether patriotism can foster social exclusion or unthinking loyalty. The theory underpins the empirical analyses presented in later chapters.