Spaces of Continuous and Measurable Functions Invariant under a Group Action

In this paper we characterize spaces of continuous and $L^p$-functions on a compact Hausdorff space that are invariant under a transitive and continuous group action. This work generalizes Nagel and Rudin's 1976 results concerning unitarily and M\"obius invariant spaces of continuous and measurable functions defined on the unit sphere in $\mathbb{C}^n$.