  Reconfigurable intelligent surfaces (RISs) are seen as a key enabler low-cost
and energy-efficient technology for 6G radio communication and localization. In
this paper, we aim to provide a comprehensive overview of the current research
progress on the RIS technology in radio localization for 6G. Particularly, we
discuss the RIS-assisted radio localization taxonomy and review the studies of
RIS-assisted radio localization for different network scenarios, bands of
transmission, deployment environments, as well as near-field operations. Based
on this review, we highlight the future research directions, associated
technical challenges, real-world applications, and limitations of RIS-assisted
radio localization.
