A Wellington boot, gumboot, rubber boot, rain boot, rainboot, or welly for short, is a type of waterproof boot made of rubber.

Originally a type of leather riding boot adapted from Hessian boots, a style of military foot wear, Wellington boots were worn and popularised by Arthur Wellesley, 1st Duke of Wellington. They became a staple of practical foot wear for the British aristocracy and middle class in the early 19th century. The term was subsequently applied to waterproof rubber boots ubiquitously worn today in a range of agricultural and outdoors pursuits.

The term Wellington boot comes from Arthur Wellesley, 1st Duke of Wellington, who instructed his shoemaker to create the boot by modifying the design of the Hessian boot. The terms gumboot and rubber boot are both derived from the rubber modern Wellington boots are made from, with the term "gum" coming from gum rubber.

The terms Wellington boot and gumboot are most commonly used in British English, with the term being occasionally used in American English. Instead, the terms rubber boot and rain boot are more commonly used in American English. Further, in American English, the term Wellington boot is sometimes used to specifically refer to Wellington boots with a more fashionable design.

The Duke of Wellington instructed his shoemaker, Hoby of St. James's Street, London, to modify the 18th-century Hessian boot. The resulting new boot was fabricated in soft calfskin leather, had the trim removed and was cut to fit more closely around the leg. The heels were low cut, stacked around an inch (2.5 centimetres), and the boot stopped at mid-calf. It was suitably hard-wearing for riding, yet smart enough for informal evening wear. The boot was dubbed the Wellington and the name has stuck in English ever since. In the 1815 portrait by James Lonsdale, the Duke can be seen wearing the more formal Hessian style boots, which are tasselled.

Wellington's utilitarian new boots quickly caught on with patriotic British gentlemen eager to emulate their war hero. Considered fashionable and foppish in the best circles and worn by dandies, such as Beau Brummell, they remained the main fashion for men through the 1840s. In the 1850s they were more commonly made in the calf-high version, and in the 1860s they were both superseded by the ankle boot, except for riding. Wellington is one of the two British Prime Ministers to have given his name to an item of clothing, the other being Sir Anthony Eden (see Anthony Eden hat) whilst Sir Winston Churchill gave his name to a cigar, and William Gladstone (four times prime minister between 1868 and 1894) gave his to the Gladstone Bag, the classic doctor's portmanteau.

Production of the Wellington boot was dramatically boosted with the advent of World War I and a requirement for footwear suitable for the conditions in Europe's flooded and muddy trenches. The North British Rubber Company (now Hunter Boot Ltd) was asked by the War Office to construct a boot suitable for such conditions. The mills ran day and night to produce immense quantities of these trench boots. In total, 1,185,036 pairs were made to meet the British Army's demands.^{[citation needed]}

In World War II, Hunter Boot was again requested to supply vast quantities of Wellington and thigh boots. 80% of production was of war materials, from (rubber) ground sheets to life belts and gas masks. In the Netherlands, the British forces were working in flooded conditions which demanded Wellingtons and thigh boots in vast supplies.