This paper demonstrates how policy-specific characteristics affect inter-municipal cooperation. We investigate if a municipality’s cooperation activity in a policy area hinges on whether the policy is considered relevant or politicized by local officials. Using data from two surveys of Swiss local administrators and officials conducted in 2017 that include detailed questions on public service provision, we find that the perceived relevance of a policy for a municipality is associated with more inter-municipal cooperation whereas perceived politicization goes along with less inter-municipal cooperation. These results suggest that policy-specific characteristics play a crucial role for understanding inter-municipal cooperation.