Triboelectric nanogenerators (TENGs) have recently enjoyed rapid development due to their easy fabrication, stable outputs, and wide range of applications. By combining conventional textiles with TENGs, textile-based TENGs (t-TENGs) can be employed with wearable devices and smart textiles. The t-TENGs with a yarn structure, triboelectric yarns, can be directly used to conduct energy conversion and be processed into other energy-harvesting textile structures due to their lightweight, flexibility, and processability. This review summarizes the research progress in triboelectric yarns. It starts with a systematic discussion of the working mechanism and manufacturing materials of triboelectric yarns. Subsequently, we discuss the four major methods of constructing triboelectric yarns including twisting/wrapping, coating, electrospinning, and other/composite methods. In particular, details about the energy harvesting performance, the triboelectric yarns' physical properties, and weaving/knitting capability are given. Finally, comments and perspectives are provided for the future design of high-performance triboelectric yarns.