This special issue of the journal is entirely devoted to subnational constitutionalism. To do so, it tries to adopt a comparative and interdisciplinary perspective and to identify constitutional patterns in those federal or regional contexts where subnational polities do not have a legal document formally called “constitution”. Some contributions have a national focus (on Belgium, Spain, Germany, Argentina, Ethiopia, and Macao). Other pieces, instead, consider the phenomenon from a comparative perspective, focusing on the external relations of subnational polities, the distinctive aspects of legislatures and legislative power at this institutional level, and the role of ordinary and constitutional judges.