A PCT in London is the first in the country to move ahead with a phased handover of budgetary control.
GPs working for NHS Redbridge will decide how and where money is spent on healthcare.
Five polysystems have replaced the north-east London borough's three practice-based commissioning clusters. They were in charge of representing the 51 practices that fall within the NHS Redbridge area.
Once the handover is complete, the GP-led network will have control of a budget of around £400m.
The care professionals will be responsible for commissioning services and meeting health targets set by the Department of Health and NHS Redbridge.
Each polysystem covers a distinct geographical area of the borough and is managed by a polyboard made up of local GPs. The polysystems are each designed around a "hub and spoke" model.
A multipurpose polyclinic sits at the heart or hub of each polysystem with surrounding GP surgeries, pharmacies and hospitals forming the spokes to create a seamless level of integrated care.
The polyclinics will offer a wide range of health services under one roof, including many traditionally hospital-based services, such as diagnostics and outpatient appointments.
Local GP Narinder Sharma, clinical director for Loxford Polysystem, said: "Health needs vary from area to area and being able to focus the appropriate resources on specific areas as well as anticipate future health trends is a great step forward."