NHS England is the administrative body which manages how health services up and down the country are run. It is made up primarily of managers and officials, not the doctors and nurses providing care in hospitals.
The government provides it with money and tells it what its priorities are for the health service - for example, that might be cutting waiting times or improving cancer survival rates.
NHS England's role is to funnel the money it is given into different parts of the health service and work out how to juggle resources in order to bring about the change the government wants to see.
In 2012, NHS England was given more independence by the Conservative-led government. They said doing so would prevent politicians from interfering too much in how front line services are run - but critics say that change has made it harder to carry out reform or drive improvement.
Prime Minister Sir Keir Starmer believes that overhauling management structures will put NHS in England "back into democratic control" and free up money for front-line services.
NHS England is also responsible for other functions like overseeing training and collecting data, as well as managing GP services.
There are separate organisations in Scotland, Wales and Northern Ireland, so these changes only impact England.