A recurrent theme in the literature on advisory groups is the belief that think tanks, policy-planning groups and advisory units of one sort or another invariably fail to fulfil their objectives and have only a limited influence on policy outcomes. The principal reason given for this is that advisory groups are subjected to strong bureaucratic pressures and are frequently 'neutralized' or rendered ineffec tive by their institutional environment. It is also contended that longer-term policy groups commonly suffer an additional problem in that they lack sufficient political support. This thesis evaluates these claims by undertaking a comparative study of the Australian Priorities Review Staff (1973-76) created by Labor Government of Gough Whitlam, and the New Zealand Prime Minister's Advisory Group (1975 -) established by the National Government of Robert Muldoon. The origins, structure and operations of both groups are examined in detail, and the problems encountered by each group are identified and explained. The research is based on a series of 87 in-depth interviews conducted during 1978 and 1979. Those interviewed included senior politicians, civil servants and advisory group members (both past and. present) in Australia and New Zealand. The author also spent three months working in the New Zealand Treasury as a researcher-participant. The thesis concludes that small advisory groups are indeed constrained by powerful bureaucratic forces and conventions. However, it is argued that these forces are not usually debilitating and that their operation does not provide a sufficient explanation for the lack of effectiveness experienced by some groups. Instead, it is contended that a group's influence on policy outcomes is largely dependent on its level of political support. This support is itself contingent on several other factors including the politician's need for the group, his relationship with the group's director, the quality of the staff and the type of functions undertaken by the group.