1 INTRODUCTION TO THE SPECIAL ISSUE: ASSEMBLAGES OF POLICY EXPERTISE THEN AND NOW This special issue adds to a growing set of studies that have recently engaged with the themes of policy advice, expertise, and policy advisory systems (PASs); or, in other words, with the assemblages of advisory units and practices that exist around governments at a given time and with which governments and other actors engage for policy purposes (Craft & Halligan, 2020; Plowden, 1987).