The institutionalization of the role of ministerial advisers in most parliamentary democracies has transformed what was once a pas de deux between ministers and senior civil servants into a menage a trois. This article assesses the impact of ministerial advisers on the contest of policy ideas. It makes a theoretical case for paying closer attention to this issue than has thus far been the case, and assesses civil servants’ perceptions of advisers’ influence on contestability. The core conclusion, which is at variance with much of the scholarship on ministerial advisers, is that advisers pose a greater threat to policy contestability than to civil service impartiality.