This edited volume examines Europe’s (sub)regional groupings – Benelux, Nordic Council, Baltic Group, Visegrád Four, and EU Med – as nested institutions interacting with, complementing, or contesting EU integration. Framed by shelter theory and differentiated integration, the book assesses their historical origins, institutionalisation, functions (vanguard, functional cooperation, coordination, resistance), and effects on EU policymaking. Part I revisits Benelux as laboratory and model across internal market, JHA, defence, and police cooperation; Part II surveys other groupings and macro-regional strategies. Through comparative case studies, it tests expectations about the regularity of meetings, institutionalisation, and policy ambitions to understand when and how smaller states leverage regional coalitions to shape Europe today. A must-read for anyone interested in the underexplored engines of European integration – especially in an era of renewed geopolitical tension and shifting alliances.

Contributors are: Robert Harmsen, Anna-Lena Högenauer, Spero Simeon Z. Paravantes, Alain De Muyser, Mendeltje van Keulen, Pierluigi Simone, Paweł Kołek, Martin Dangerfield, Stefan Gänzle, Jörg Mirtl, Matthew Broad, Daunis Auers, Giorgio Oikonomou, Napoleon Maravegias, and Melanie H. Ram.