Abstract: Given a finite group $G$ and action $\sigma$ of $G$ on a finite set $S$, the $G-\sigma$ circulant ring is the ring of $S \times S$ matrices invariant under the induced action of $G$ on $S \times S$ and hence on $M_{S,S}$. We will see that this provides a generalization not only of circulant and $G$ circulant matrices but also the recently defined notion of a join of group rings. This provides a new approach to investigating an important family of matrices which have found many multidisciplinary applications. Several examples of generalizations to this context of properties of join rings will be given.