- This contribution conceptualises bottom-up politicisation in Europe’s multi-level system. EU-level actors, we argue, respond strategically to the functional and political pressures ‘travelling up’ from the member states. Perceiving domestic dissensus as either constraining or enabling, actors display both self-restraint and assertiveness in their responses. Motivated by the survival of the EU as a system ‘under attack’, and by the preservation of their own substantive and procedural powers, actors choose to either politicise or depoliticise decision-making, behaviour and policy outcomes at the supranational level. As a collection, this Special Issue demonstrate that the choices actors make ‘under stress’ at the EU-level – ranging from ‘restrained depoliticisation’ to ‘assertive politicisation’ – are, indeed, conditional on how bottom-up pressures are perceived and processed.