Why do some people belong and others do not? What does it take to be accepted? Who decides? Based on what justification? takes a bracing look at a frequently debated question, as personal as it is political. Rising migration flows, escalating global conflicts, faltering democracies, and polarizing politics have made the question "who is in and who is out?" one of the most urgent issues of our time. With the goal of improving mutual understanding and achieving meaningful shifts in personal and policy-level discussions, the author holds a critical lens to widely held assumptions about the role of diversity and inclusion in society, our relationship to biases, and the many and seemingly contradictory forms equity can take. Questions around belonging release emotions and muddy our judgment, dampening our ability to think clearly. A better understanding of the "mechanics" of belonging can help individuals and institutions make decisions and engage with each other.