The personal coat of arms, or the "armorial achievement," usually has several components: the shield, the helm, the mantling and the crest.

The most important -- and the only essential -- component of the achievement is the shield. If there is a crest, it is usually displayed on a twisted cloth called a torse, which is attached to a helm. Attached to the helm beneath the crest is mantling, which represents the cloth used as protection from the sun. The optional motto is usually shown on a scroll beneath the shield, except in Scotland where it is shown above the crest.
Heraldry has many historical origins. In early medieval northern Europe, people often used pictorial housemarks to identify their property because few could read or write. These pre-heraldic designs were adopted by succeeding generations of the same family in a time when surnames were not widely used. The ancient Celtic clans used colors to indicate social and political standing. Early Viking helmets show the use of crests (decorated helmets). Inherited, identifying banners and devices were used in battle by descendants of Charlemagne in the 11th century A.D.
The colorful shields, helms, and crests we are familiar with today had their origins around the mid-12th century in Europe, when heralds traveled from town to town to organize military tournaments. Heralds soon became experts at identifying competitors' shields, crests, and banners and they began recording the designs. They developed a specialized language in which they could concisely and accurately "blazon" or describe arms. Over several hundred years, heraldry gradually developed into a highly sophisticated art.
Today, the use of heraldry permeates American life. Heraldic designs are used by sports teams, police, cities, counties, states, federal agencies, the military, schools, churches, corporations, and others.
In some countries, the government authorizes "grants" of heraldic designs to individuals or organizations. Such authorities exist in England, Wales, Northern Ireland (The College of Arms), Ireland (The Chief Herald of Ireland), Scotland (The Court of the Lord Lyon), and Canada (The Canadian Heraldic Authority). The rules are strictest in Scotland and England, where it is illegal to freely assume arms. However, in most countries including the U.S.A., one can legally assume any coat of arms one chooses (unless one infringes on a business trademark). No matter what the law, using someone else's arms is dishonorable because it is akin to stealing a corporate logo for one's own use.
Heraldry is popular in the U.S.A., especially with the growing interest in genealogy. Tracing one's roots to an ancestor who bore arms can be an exciting discovery. However, the fact that a foreign ancestor bore arms probably does not give one the right to bear the ancestor's arms under the "old country's" laws. Usually, one must be in the male line of descent, and in Scotland the line must be in a line of first born sons.
There are hundreds of businesses in the U.S.A. that sell "surname" arms. Most of these arms usually are in no way connected to the purchaser. These businesses claim that because the purchaser has a certain surname, he is entitled to bear the arms or has descended from an ancestor of the same name. There is no truth to these claims (except by unlikely coincidence). The sale of "surname arms" involves the dishonorable practice of usurping someone else's heraldic identity. U.S. citizens are free to adopt any arms, but should respect others by not "stealing" them from others.
U.S. citizens are free to pass arms to their children -- sons and daughters -- and to use the arms of their ancestors. When doing so, one should respect the traditions of foreign ancestors by adopting arms according to the traditions in the home country, which usually means honoring succession along a well-documented paternal line. For the vast majority of U.S. citizens, proving descent from a distant ancestor who bore arms is very difficult. In most cases, if your father or paternal grandfather did not have a coat of arms, it is best to design your own and to start your own heraldic legacy.