Moulding is nonstructural, and is used to decorate structural elements and create ornamental effects with light and shadow. Ancient Greeks used moulding in their buildings to divide surfaces into smaller parts to create visual interest, generally basing their profiles on the ellipse, parabola or hyperbola. Romans simplified the mouldings of the Greeks, basing their profiles instead on the circle. These two styles of moulding evolved into eight classical shapes of moulding, derived from complex mouldings which have irregular curvatures, and simple mouldings which are formed from a continuous curve such as the arc of a circle. These profiles became the basic building blocks of interior ornament for centuries.

Until the middle of the 1800's, most moulding in America was made on the building site by carpenters who used hand planes, chisles and gouges. Wide pieces of trim, such as crown moulding, were made in woodworking shops where large planes were pulled by apprentices under the guidance of master artisans. Depending on the size and style of a building, moulding could be used to ornament almost all the interior architectural elements. Ornamentation cost money, however, so the extent to which it was used in a building was a good indication of the wealth of the building's owner.

By the 1850's planing machines had been developed to produce moulding on a large scale, at a much lower cost than handmade moulding. Soon new planing mills powered by water and steam were established. This made elaborate and sophisticated ornamentation available to all who wanted it in their homes. Carpenters combined the machine made mouldings to create an infinite variety of complex three-dimensional profiles. Moulding profiles could be easily changed with the fashion, and not only reflected the prevailing style of the time, but become a significant element of the styles of the decorative periods.

The widepread use of decorative moulding continued until after World War 1, when buildings began to be designed without a historial reference. Mouldings were simplified, and some, like casings and baseboards, totally lost their classical character and reference. Many modern interiors became generic, without the individuality that the use of classic moulding brings to interior architecture. Fortunately, small millworks keep alive the tradition of classical moulding, making it still possible to use unique decorative moulding in the home and workplace.