The advent of sixth-generation (6G) wireless networks holds the promise of revolutionizing the landscape of the Internet of Things (IoT), expanding the horizons of wireless communication and ushering in a new era of IoT applications with unprecedented performance and reliability. However, a crucial requirement in this field is the need for precise positioning and localization of IoT devices, which is a fundamental necessity for a plethora of applications. Nevertheless, the existing positioning and localization methods used in 6G-IoT pose challenges due to blockages of the line-of-sight signals and interference and difficulties arising from multipath propagation, which results in new requirements for positioning and localization. These fundamental necessities for precise positioning and localization can be fulfilled with a reconfigurable intelligent surface (RIS), a potential candidate technology for the future 6G wireless communication. Thus, integrating RIS in the IoT can enhance the accuracy of positioning while offering the added benefits of being economical and energy-efficient. In this chapter, the role of RIS-assisted 6G-IoT networks in wireless positioning and localization is explained initially. Then, the fundamental localization principles and the RIS-aided localization algorithms are explored. After that, the state-of-the-art research on positioning and localization, comprising RIS-assisted millimeter-wave positioning systems, RIS for indoor, near-field, outdoor, and far-field localization, and RIS for terahertz communication, is elaborated in detail. Finally, this chapter concludes by discussing the potential challenges and future research directions of RIS-aided 6G-IoT for wireless positioning and localization.