William Henry Fox Talbot (/tælbət/; 11 February 1800 – 17 September 1877) was an English scientist, inventor, and photography pioneer who invented the salted paper and calotype processes, precursors to photographic processes of the later 19th and 20th centuries. His work in the 1840s on photomechanical reproduction led to the creation of the photoglyphic engraving process, the precursor to photogravure. He was the holder of a controversial patent that affected the early development of commercial photography in Britain. He was also a noted photographer who contributed to the development of photography as an artistic medium. He published The Pencil of Nature (1844–1846), which was illustrated with original salted paper prints from his calotype negatives and made some important early photographs of Oxford, Paris, Reading, and York.

A polymath, Talbot was elected to the Royal Society in 1831 for his work on the integral calculus, and researched in optics, chemistry, electricity and other subjects such as etymology, the decipherment of cuneiform, and ancient history.

Talbot was born in Melbury House in Dorset and was the only child of William Davenport Talbot, of Lacock Abbey, near Chippenham, Wiltshire, and his wife Lady Elisabeth Fox Strangways, daughter of the 2nd Earl of Ilchester. His governess was Agnes Porter who had also educated his mother. Talbot was educated at Rottingdean and at Harrow School. During this period he developed an interest in botany, especially mosses, which he studied with several members of his family, and was supported and encouraged by the botanists Lewis Weston Dillwyn, James Dalton and William Jackson Hooker. He was later educated at Trinity College, Cambridge, where he was awarded the Porson Prize in Classics in 1820, and graduated as twelfth wrangler in 1821. From 1822 to 1872, he communicated papers to the Royal Society, many of them on mathematical subjects. At an early period, he began optical research, which later bore fruit in connection with photography. To the Edinburgh Philosophical Journal in 1826 he contributed a paper on "Some Experiments on Coloured Flame"; to the Quarterly Journal of Science in 1827 a paper on "Monochromatic Light"; and to the Philosophical Magazine papers on chemical subjects, including one on "Chemical Changes of Colour".

Talbot invented a process for creating reasonably light-fast and permanent photographs that was the first made available to the public; however, his was neither the first such process invented nor the first one publicly announced.

Shortly after Louis Daguerre's invention of the daguerreotype was announced in early January 1839, without details, Talbot asserted priority of invention based on experiments he had begun in early 1834. At a Friday Evening Discourse at the Royal Institution on 25 January 1839, Talbot exhibited several paper photographs he had made in 1835. Within a fortnight, he communicated the general nature of his process to the Royal Society, followed by more complete details a few weeks later. Daguerre did not publicly reveal any useful details until mid-August, although by the spring it had become clear that his process and Talbot's were very different.

Talbot's early "salted paper" or "photogenic drawing" process^, used writing paper bathed in a weak solution of ordinary table salt (sodium chloride), dried, then brushed on one side with a strong solution of silver nitrate, which created a tenacious coating of very light-sensitive silver chloride that darkened where it was exposed to light. Whether used to create shadow image photograms by placing objects on it and setting it out in the sunlight, or to capture the dim images formed by a lens in a camera, it was a "printing out" process, meaning that the exposure had to continue until the desired degree of darkening had been produced. In the case of camera images, that could require an exposure of an hour or two if something more than a silhouette of objects against a bright sky was wanted. Earlier experimenters such as Thomas Wedgwood and Nicéphore Niépce had captured shadows and camera images with silver salts years before, but they could find no way to prevent their photographs from fatally darkening all over when exposed to daylight. Talbot devised several ways of chemically stabilizing his results, making them sufficiently insensitive to further exposure that direct sunlight could be used to print the negative image produced in the camera onto another sheet of salted paper, creating a positive.

The "calotype", or "talbotype", was a "developing out" process, Talbot's improvement of his earlier photogenic drawing process by the use of a different silver salt (silver iodide instead of silver chloride) and a developing agent (gallic acid and silver nitrate) to bring out an invisibly slight "latent" image on the exposed paper. This reduced the required exposure time in the camera to only a minute or two for subjects in bright sunlight. The translucent calotype negative made it possible to produce as many positive prints as desired by simple contact printing, whereas the daguerreotype was an opaque direct positive that could be reproduced only by being copied with a camera. On the other hand, the calotype, despite waxing of the negative to make the image clearer, still was not pin-sharp like the metallic daguerreotype, because the paper fibres blurred the printed image. The simpler salted paper process was normally used when making prints from calotype negatives.

Talbot announced his calotype process in 1841, and in August he licensed Henry Collen, the miniature painter, as the first professional calotypist. The most celebrated practitioners of the process were Hill & Adamson. Another notable calotypist was Levett Landon Boscawen Ibbetson.