A CNT yarn is a collection of interlocked CNTs which form a long and continuous fiber of macroscopic scale. CNT yarns of more than a kilometer are now available so that they have been drawing ever-growing attention from the scientific community. In principle, CNT yarns can inherit the excellent electrical, mechanical and chemical properties of CNTs provided they are produced perfectly. In this perspective review, the production methods of CNT yarns are extensively investigated and reported in detail. Although CNT yarns have a great potential to revolutionize our future, it can only be possible by improving their essential material properties such as tensile strength and edectrical conductivity.