Hampshire and Thames Valley Police forces to begin joint work
Hampshire and Thames Valley Police are due to begin working together as part of cost-cutting measures that may see more than 100 posts close.
The two authorities have signed a legal agreement under the Police Act 1996 covering how they will share resources.
The Joint Roads Policing Unit is expected to become the first department to merge, at the end of January.
Joint operations and joint firearms units will follow. No jobs will be lost but vacant posts will not be filled.
The Thames Valley Police Federation has previously said the sharing of the two authorities' resources raised questions about the possible amalgamation of whole forces.
A Hampshire Constabulary spokeswoman said the agreement would not lead to officers being made redundant but posts would be closed.
"We are not cutting jobs," she said but added, "we might not recruit for a while".
Ch Supt Chris Shead, of Hampshire Constabulary which hosts the joint departments, said the move would result "in greater efficiency and the delivery of a service that both forces can be proud of".
The two forces, which cover Hampshire, Isle of Wight, Berkshire, Oxfordshire and Buckinghamshire, decided to share resources in November 2010.
The joint firearms unit will be the last to form, after the 2012 London Olympics.
The joint operations unit includes resources such as dogs and training.