In the US system of decentralized federalism, competitive dynamics among local governments are not incompatible with successful interlocal collaboration. Municipalities often collaborate with competing jurisdictions in the same region to provide services and solve problems. Yet, competitive relations among municipalities are expected to complicate collaboration, escalating transaction costs due to divergent goals and lack of trust. This article uses the Institutional Collective Action framework to examine the conditions under which local governments are best able to surmount competition-related hurdles and successfully partner with their chief municipal competitors. An original survey of mayors and councilors is used to test potential predictors of collaboration among top competitors. Results show that municipalities often collaborate with their chief competitors but are less likely to do so when they are situated in municipally-fragmented regions, when they are located in a different county from their top competitors, and when they are fiscally strong.