With the 30th anniversary of the policy advisory systems concept on the horizon, it is an appropriate time to reflect further on the concept’s utility, particularly in helping to understand the dynamics of system change and their implications for policy-making. This article provides diachronic analysis of the policy advisory systems in the classic Anglo-Saxon ‘Westminster’ family (Canada, UK, Australia, New Zealand). Analysis focuses on five advisory units: the public service and central agencies, partisan ministerial advisers, external consultants, commissions of inquiry, and select special advisory bodies. The principle research aim is to compare these cases to shed light on advisory system dynamics through identification and analysis of shared and country-specific patterns of PAS change. We argue that the leading dynamics of politicization and externalization often used to characterize how advisory systems change masks idiosyncratic country patterns. We argue that differences in the tempo, intensity, and sequencing of advisory unit (de)institutionalization are clear in these cases and that attention to these dimensions of advisory system change add precision to understanding the organization, operation, and evolution of these systems.