It is a common assumption that municipalities can increase efficiency of public services by cooperating with their neighbours. Cooperation could also help municipalities that have simply become too small to perform certain complex tasks independently. As such, cooperation has become a popular method for municipalities in large parts of the world to cope with the new demands their environment places on them. This dissertation presents a mixed method study with empirical evidence on the effects that intermunicipal cooperation has had on local public service provision within the Netherlands. It first presents a quantitative analysis of the effect that cooperation has had on municipal spending. It also explores whether any effect on spending is impacted by the size of the municipality, and it distinguishes between the effects of cooperation for different tasks – tax collection, garbage collection and social services. This analysis shows that cooperation does not reduce spending for Dutch municipalities, regardless of size or task. Tax collection is the only exception, where a reduction in associated spending is found. This analysis is followed by two in-depth case studies that explore cooperation for tax collection and social services, and provide insights into the underlying mechanisms that contribute to potential efficiency gains for these two policy areas.