BackgroundThe wide-ranging program of reforms brought about by the Health and Social Care Act (2012) in England fundamentally changed the operation of the public health system, moving responsibility for the commissioning and delivery of services from the National Health Service to locally elected councils and a new national public health agency. This paper explores the ways in which the reforms have altered public health commissioning.MethodsWe conducted multi-methods research over 33 months, incorporating national surveys of Directors of Public Health and local council elected members at two time-points, and in-depth case studies in five purposively selected geographical areas.ResultsPublic health commissioning responsibilities have changed and become more fragmented, being split amongst a range of different organisations, most of which were newly created in 2013. There is much change in the way public health commissioning is done, in who is doing it, and in what is commissioned, since the reforms. There is wider consultation on decisions in the local council setting than in the NHS, and elected members now have a strong influence on public health prioritisation. There is more (and different) scrutiny being applied to public health contracts, and most councils have embarked on wide-ranging changes to the health improvement services they commission. Public health money is being used in different ways as councils are adapting to increasing financial constraint.ConclusionsOur findings suggest that, while some of the intended opportunities to improve population health and create a more joined-up system with clearer leadership have been achieved, fragmentation, dispersed decision-making and uncertainties regarding funding remain significant challenges. There have been profound changes in commissioning processes, with consequences for what health improvement services are ultimately commissioned. Time (and further research) will tell if any of these changes lead to improved population health outcomes and reduced health inequalities, but many of the opportunities brought about by the reforms are threatened by the continued flux in the system.