What do Prime Minister's/ President's Offices do?
OECD report focusing on the centre of government - the support structure serving the highest level of the executive branch of government (presidents, prime ministers and their equivalents). The report finds that despite differences among countries in terms of constitutional forms and administrative traditions – even the extent to which the centre is led and staffed by political appointees rather than career civil servants – there are strong similarities in the functions the centre performs.
For more information see: https://www.oecd.org/gov/centre-stage-the-organisation-and-functions-of-the-centre-of-government.htm