Internal non-public service sources of policy advice cover parliamentary committees, public inquiries and other bodies that operate within the broader public sector. Some units have substantial independence, while others may be at the beck and call of ministers. The spectrum ranges from bodies located within government with permanent standing to those existing under ad hoc arrangements that may include external actors. Advice is distinguished by whether it is solicited or not, the former being commissioned by government (e.g. taskforces) and the latter being about the capacity to influence policy. Three categories of alternative policy advice within government are independent policy advisory bodies; agencies that report to parliament rather than the executive; and ad hoc entities that operate as extensions to government and comprise a range of government appointed inquiry forms.Each has changed with implications for the policy advisory system, although depoliticisation and politicisation are factors. The institutionalisation of independent standing bodies is notable. The trend to flexible instruments has allowed governments to reduce reliance on formal and independent public reviews. The expansion and contraction of alternative sources of advice has occurred over time and varies between countries, but the broad trends have been similar.