Yarns are key building blocks to construct complicated fibrous structures for diverse applications. Nanofibre yarns are expected to uncover new opportunities for development of well-defined three-dimensional nano fibrous architectures with new or enhanced functions and better mechanical performances. This book covers the recent research development in nanofibre yarns and the mechanical properties of a nanofibre yarn that is prepared by a simple twist technique. The production of short nanofibres and short nanofibre-carbon nanotube composites are also introduced in the book.