Whatever the origins of the clans -- some with Norman roots, intermarried into Celtic society; some of Norse origin, the product of Viking raids on Scotland; others traceable to the monastic system; yet others possibly descended from Pictish tribes -- by the 13th century the clan system was at the heart of Gaelic tribal culture. By the 15th century the clan chiefs of the Scottish Highlands were a threat even to the authority of the Stewart monarchs.
The word clann means "family" or "children" in Gaelic, and it was the custom for clan chiefs to board out their sons among nearby families, a practice that helped to bond the clan unit and create strong allegiances: the chief became "father" of the tribe and was owed loyalty by lesser chiefs and ordinary clansmen.
The clan chiefs' need for strong men-at-arms, fast-running messengers, and bards for entertainment and the preservation of clan genealogy was the probable origin of the Highland Games, still celebrated in many Highland communities each year, and which are an otherwise rather inexplicable mix of sports, music, and dance.
Gradually, by the 18th century, increasing knowledge of Lowland agricultural improvements, and better roads into the Highlands that improved communication of ideas and "southern" ways, began to weaken the clan system: fine clothes, French wines, and even a Lowland education became more common in chiefly households. Even before Culloden, where Bonnie Prince Charles, supported by some of the clans, was defeated by George II's army, the clan system had lost its tight grip on the Highlands. After Culloden, as more modern economic influences took hold, those on the "wrong" side lost all; many chiefs lost their lands, tartan was banned, and clan culture withered.
Tartan's own origins as a part of the clan system are disputed; the Gaelic word for striped cloth is breacan -- piebald or spotted -- so even the word itself is not Highland. However, it is indisputable that in the days before mass manufacture, when cloth was locally spun, woven, and dyed using plant derivatives, each neighborhood would have different dyestuffs -- bilberry, iris, bramble, water lily -- and therefore different colors available. In this way, particular combinations of colors and favorite patterns of the local weavers could become associated with a particular area and therefore clan, but were not in any sense a clan's "own by exclusive right."
Between 1746 and 1782 the wearing of tartan was generally prohibited. By the time the ban was lifted, many recipes for dyes and weaving patterns had been forgotten. In addition, some neighborhoods stopped making and coloring their own cloth because of the mechanization and use of chemical dyes in cloth production.
It took the influence of Sir Walter Scott, with his romantic, and fashionable, view of Highland history, to create the "modern myth" of clans and tartan. Sir Walter engineered George IV's visit to Scotland in 1822, which turned into a tartan extravaganza. The idea of one tartan or group of tartans "belonging" to one particular clan was created at this time -- literally created, with new patterns and color ways dreamed up and "assigned" to particular clans. Queen Victoria and Prince Albert reinforced the tartan culture later in the century.
It is considered "proper" in some circles to wear the "right" tartan, that is, that of your clan.
You may be able to find a clan connection with the expertise such as that available at Scotland's Clan Tartan Centre (70-74 Bangor Rd., Leith, Edinburgh. 0131/553-5161).