Nationalism has long been a normatively and empirically contested concept, associated with democratic revolutions and public goods provision, but also with xenophobia, genocide, and wars. Moving beyond facile distinctions between 'good' and 'bad' nationalisms, the authors argue that nationalism is an empirically variegated ideology. Definitional disagreements, Eurocentric conceptualizations, and linear associations between ethnicity and nationalism have hampered our ability to synthesize insights. This Element proposes that nationalism can be broken down productively into parts based on three key questions: (1) Does a nation exist? (2) How do national narratives vary? (3) When do national narratives matter? The answers to these questions generate five dimensions along which nationalism varies: elite fragmentation and popular fragmentation of national communities; ascriptiveness and thickness of national narratives; and salience of national identities.