This Palgrave Policy Essential maps and assesses key changes in the Whitehall model over the last two decades. It argues that the traditional Whitehall model is being replaced by a system of ‘New Political Governance’ (NPG) centred on politicised campaigning; the growth of political advisory staff relative to the permanent civil service; the personalisation of bureaucratic appointments; and the creation of a government machine that is ‘promiscuously partisan’. It provides a snapshot of the institutional changes that are unfolding at a critical moment, as Whitehall prepares to support Ministers in carrying out the Brexit process while addressing a series of long-term structural challenges from the demographic pressures of the ageing society to the impact of climate change. Austerity since 2010 has had a further transformative effect on Whitehall, with drastic reductions in the civil service workforce, the restructuring of government agencies, and a reconfiguration of the traditional roles and responsibilities of the permanent civil service.