This article validates the Regional Authority Index with seven widely used decentralization indices in the literature. A principal axis analysis reveals a common structure. The major source of disagreement between the Regional Authority Index and the other indices stems from the fact that the Regional Authority Index does not include local governance whereas most other indices do. Two other sources of disagreement concern the treatment of federal versus non-federal countries, and countries which have recently regionalized and/or have asymmetrical regions, whereby the more fine-grained Regional Authority index captures greater variation. The second part discusses content validity of fiscal indicators.