  This article focuses on the exploitation of reconfigurable intelligent
surfaces (RISs) in multi-user networks employing orthogonal multiple access
(OMA) or non-orthogonal multiple access (NOMA), with an emphasis on
investigating the interplay between NOMA and RIS. Depending on whether the RIS
reflection coefficients can be adjusted only once or multiple times during one
transmission, we distinguish between static and dynamic RIS configurations. In
particular, the capacity region of RIS aided single-antenna NOMA networks is
characterized and compared with the OMA rate region from an
information-theoretic perspective, revealing that the dynamic RIS configuration
is capacity-achieving. Then, the impact of the RIS deployment location on the
performance of different multiple access schemes is investigated, which reveals
that asymmetric and symmetric deployment strategies are preferable for NOMA and
OMA, respectively. Furthermore, for RIS aided multiple-antenna NOMA networks,
three novel joint active and passive beamformer designs are proposed based on
both beamformer based and cluster based strategies. Finally, open research
problems for RIS-NOMA networks are highlighted.
