Early American
The earliest known piece of American furniture is a chest of drawers made around 1660. It's very rectangular and has a distinctive carved frame-and-panel construction. Altough it  is reminiscent of earlier British" Age of Oak" pieces, it is recognized  as a distinctly American in style. Many other early Colonial era pieces, such as wainscot chairs and heavy joint-tables, are similarly in the "Age of Oak"  tradition.

By the end of the period, the influence of the British William and Mary style was being felt. Compared to earlier Jacobean and Carolean pieces this was a much lighter, more elegant style. Inverted cup-turned legs, bun feet, and serpentine stretchers make this style very identifiable, especially in comparison with the Queen Anne style that followed, marking the beginning of the 18th century.

The 18th Century
To understand the term "18th-century furniture," it is most informative to refer to the following terms, all of which may also be defined as 18th century: William and Mary, Queen Anne, Georgian, Chippendale, Hepplewhite, Sheraton, Adam, Regency, Federal, and the French periods of the Louis, Directoire, and Empire.

In essence, however, all 18th-century furniture, whether American, British, or French...and there is much connection between the first two and a great deal of dependence of these two on the latter  all share an informed and purposely trained construction that is distinct from a lot of  subsequent furniture. There is both less of the unrestrained commercialism typical of the mass-produced furniture of the 19th century with its never ending "Revival" styles, and less of the often self-indulgent estheticism of so-called studio or art furniture typical of the 20th century.

Eighteenth-century furniture may be commonly thought of as representing the golden age of the cabinetmaker, trained in the "Arts and Mysteries of the Craft," which manifests as highly finished, sophisticated designs, albeit stylistically often as widely divergent from one another as is a cabriole leg from a Federal taper.

The 19th Century
The 19th century is marked by the Industrial Revolution, which caused profound changes in society. With increased working populations in cities, the rise of a new class of wealthy (but not necessarily informed) furniture buyers, together with the arrival of mass-production and the consequent demise of the individual craftsman-designer, the gradual progression of furniture styles that had characterized previous centuries was replaced by a riot of often poorly imitated styles.

Since mass-production of parts became easy and inexpensive, it was a simple matter to graft more or less historically correct ornaments onto all sorts of furniture, thereby making possible a continual stream of "revival" styles to feed the public’s appetite. The result was a century of furniture whose commonest denominator was excessive ornament in the form of applied metal or wood carvings, inlays, or stencils, marketed variously under the guise of so-called Rococo Revival, Gothic Revival, Renaissance and Italian Revivals, Greek, Roman, and Egyptian Revivals, and even various Eastern Revivals.

20th Century
The term"20th Century" is only very generally useful, since it includes so many distinct styles more helpful when understood on their own. But it can mean anything produced after the 19th century, representing relatively contemporary furniture, as opposed to period furniture.

Styles such as Art Nouveau and Art Deco, while remaining useful inspirations for subsequent 20th-century styles, are quite distinct from most Modern and Post-modern furniture, and none of the above can be considered as quintessentially representative of the20th century.

The fact is, however, that due the availability of a much larger choice of materials than ever before, and because of an increased awareness of historical and cross-cultural esthetics, 20th-century furniture is perhaps more diverse, in terms of style, than the entire three centuries that preceded it.