Towards double-elliptic integrable systems: a review

A review of the $p,q$-duality for systems of the Calogero-Ruijsenaars type will be given including a partial description of the elliptic-trigonometric system dual to the elliptic Ruijsenaars one. Approaches to constructing a double-elliptic system will be also discussed, as well as a relation with the bi-elliptic Koroteev-Shakirov model.