Tartan is a patterned cloth consisting of crisscrossed, horizontal and vertical bands in multiple colours. Tartans originated in woven wool, but now they are made in many other materials. Tartan is particularly associated with Scotland; Scottish kilts almost always have tartan patterns. Tartan is made with alternating bands of coloured (pre-dyed) threads woven as both warp and weft at right angles to each other. The weft is woven in a simple twill, two over—two under the warp, advancing one thread at each pass. This forms visible diagonal lines where different colours cross, which give the appearance of new colours blended from the original ones. The resulting blocks of colour repeat vertically and horizontally in a distinctive pattern of squares and lines known as a sett.

Tartan is often mistakenly called "plaid" (particularly in North America), but in Scotland, a plaid is a large piece of tartan cloth, worn as a type of kilt or large shawl. The term plaid is also used in Scotland for an ordinary blanket such as one would have on a bed. The Dress Act of 1746 attempted to bring the warrior clans under government control by banning the tartan and other aspects of Gaelic culture. When the law was repealed in 1782, it was no longer ordinary Highland dress but was adopted instead as the symbolic national dress of Scotland status that was widely popularised after King George IV wore a tartan kilt in his 1822 visit to Scotland.

Until the middle of the nineteenth century, the highland tartans were only associated with either regions or districts, rather than any specific Scottish clan. This was because like other materials, tartan designs were produced by local weavers for local tastes and would usually only use the natural dyes available in that area, as synthetic dye production was non-existent and transportation of other dye materials across long distances was prohibitively expensive.