  The air-ground integrated sensing and communications (AG-ISAC) network, which
consists of unmanned aerial vehicles (UAVs) and ground terrestrial networks,
offers unique capabilities and demands special design techniques. In this
article, we provide a review on AG-ISAC, by introducing UAVs as ``relay'' nodes
for both communications and sensing to resolve the power and computation
constraints on UAVs. We first introduce an AG-ISAC framework, including the
system architecture and protocol. Four potential use cases are then discussed,
with the analysis on the characteristics and merits of AG-ISAC networks. The
research on several critical techniques for AG-ISAC is then discussed. Finally,
we present our vision of the challenges and future research directions for
AG-ISAC, to facilitate the advancement of the technology.
