Police forces in Cambridgeshire, Bedfordshire and Hertfordshire are set to work closer together in order to save £20m a year.
The three counties' chief constables have signed a document setting out which departments could merge.
The agreement sets out how the forces will collaborate and how the financial arrangements will work.
The forces hope to improve efficiency, effectiveness and resilience while protecting frontline services.
The Bedfordshire and Hertfordshire forces began collaborating in 2007 and have developed 13 joint units.
A joint procurement department has also been established for all three forces.
The three chief constables and each police authority chair have signed up to the agreement.
The forces hope to save £20m a year by the end of 2015.
Departments likely to be merged by the end of 2011 include major crime, professional standards, scientific services and firearms support.
Mergers of operational support, including call-handling, and of functions such as information technology, fleet services and legal services are likely to take longer.
Cambridgeshire Chief Constable Simon Parr said: "Working together with Bedfordshire and Hertfordshire in this way will enable us to continue to provide the highest possible levels of service to the people of Cambridgeshire."