  Intelligent Reflecting Surface (IRS) is envisioned to be a technical enabler
for the sixth-generation (6G) wireless system. Its potential lies in delivering
high performance while maintaining both power efficiency and
cost-effectiveness. Previous studies have primarily focused on point-to-point
IRS communications involving a single user. Nevertheless, a practical system
must serve multiple users simultaneously. The unique characteristics of IRS,
such as non-frequency-selective reflection and the necessity for joint
active/passive beamforming, create obstacles to the use of conventional
multiple access (MA) techniques. This motivates us to review various MA
techniques to make clear their functionalities in the presence of IRS. Through
this paper, our aim is to provide researchers with a comprehensive
understanding of challenges and available solutions, offering insights to
foster their design of efficient multiple access for IRS-aided systems.
