Spinning, final process in the transformation of fibre into yarn or thread. With the single exception of silk, all natural fibres have a limited, fairly definite length. This staple length ranges from about 1.25 cm (0.5 in) in the case of some American and Asian cottons to about 1 m (3.3 ft) in the case of some bast and leaf fibres. Most synthetic fibres are produced in cut lengths and therefore have to be spun. See Textiles; see also the separate articles on all the fibres mentioned in this article.

The object of spinning and of the processes that precede it is to transform the single fibres into a cohesive and workable continuous-length yarn. Processes that staple fibres go through vary according to the type of fibre. Cotton, wool, flax, jute, and the other natural fibres are spun in different ways, and wool and some of the bast fibres can be spun in two different ways, resulting in yarns with differing properties. Basically, in the case of natural fibres, the processing involves opening, blending, carding (in some cases also combing), drawing, and roving to produce the material for the spinning frame. This is followed by the spinning itself.

Before the age of machinery, spinning was done by hand with the spindle and distaff. The latter was a stick or staff upon which a bundle of the fibre to be spun was loosely bound, and it was either held in the left hand or stuck in the belt. The spindle was a smaller tapering rod, the rotation of which gave the twist and around which the thread was wound as it was twisted. The spinning wheel, introduced into Europe from India in the 13th or 14th century, improved on the hand-spinning method. The spindle was set horizontally in a wheel turned by a pedal and produced a single thread. Two spinnings were necessary for a very fine thread. Spinning by hand is still the principal method used in many developing countries.

The development in England of the spinning jenny (1764) by James Hargreaves, the throttle or roll-drawing machine (1769) by Richard Arkwright, and the spinning mule (1779) by Samuel Crompton revolutionized the cotton industry. The jenny enabled the spinning of a number of threads at one time, and the throttle incorporated a system of rollers to stretch out the rovings. In the mule, the spindles were set in a travelling frame to reduce the strain of the process of spinning by rollers, thus producing finer yarns. Although these processes are now obsolete, except for a few mule spindles that are still being operated, the general principles of cotton spinning today are much the same, involving the processes of opening, carding and combing, drawing, roving, and spinning. In the case of synthetic fibres, spinners in the first instance tended to use existing machinery. Thus, if they were cotton spinners they used cotton-spinning machinery that would necessitate the supply of a synthetic fibre with a staple length compatible with such machinery.

Many refinements of spinning machinery have occurred in recent years, aimed at the diversification brought by the development of so many new types of synthetic fibres, and spinning machinery exists today that can be used only for synthetic fibres. Some of the newer spinning techniques being used for synthetic fibres are basically modifications and simplifications of conventional machinery.