Chapter 5 explores the politically appointed staffs working in ministers’ and prime ministers’ offices. Comparative analysis showcases the flexibility of policy advisory systems (PAS) and the several interpretations of the Westminster tradition. Advisers were added to PAS to extend ministers’ control, address deficiencies in public service advice and increase ministers’ capacity to address the politics of policy work. Their effects have attracted debates about politicisation. At best, advisers identify political risks and help ministers avoid the derailment of policy agendas.They serve as ports of call for officials, interested stakeholders and other ministers, as well as facilitate the circulation of policy advice within government. At worst they have corrosive effects, overstepping boundaries by throwing their weight around and directing public servants without appropriate authority. They act as gatekeepers on the professional advice of the public service before it reaches ministers. There is widespread agreement that partisan advisers have become more prominent and influential. Central political offices have become adept at using them as systemic instruments to secure political alignment and coordination throughout government. Their growing numbers and the specialisation of policy functions have become important for how ministers exert political control and seek contestable policy.