The examination of Westminster policy advisory systems begins with the administrative tradition that has fundamentally shaped, and continues to influence, the practices in the four cases and the country-specific developments. The anglophone countries constitute a coherent set because of their common tradition and their close historical and ongoing associations and interactions. This overview addresses the shared characteristics of the Westminster-type system and the constituent features of government pertinent to policy advisory systems. It compares public organisation and structures and unique characteristics, focusing on political executives, the machinery of government and ancillary public sector advisory agents (e.g. parliamentary committees, commissions of inquiry). The unique characteristics of the cases are examined, such as the distinct patterns of public sector reform that have implications for policy advice and the role of central agencies vis-à-vis departments.