A sawmill or sawmill is a facility where logs are cut into lumber. Modern sawmills use a chainsaw to cut logs longitudinally to make long pieces, and longitudinally diagonally depending on standard or custom dimensions (sized lumber). The "portable" sawmill is a simple process. The log lies flat on a steel bed and the chainsaw cuts the log horizontally along the length of the bed, with the operator pushing the saw manually. The most basic type of sawmill consists of a chainsaw and a specialized apparatus ("Alaska sawmill") with similar horizontal operations.

Before the invention of the sawmill, boards were made in a variety of manual ways, either burnished (split) and planned, cut, or, more often, hand-cut with a whip by two men, one in the saw pit above and the other below. The oldest known mechanical mill is the Hierapolis sawmill, a Roman water-powered stone mill in Hierapolis in Asia Minor dating back to the 3rd century AD. Other water-powered mills followed, and in the 11th century they spread to Spain and North Africa, the Middle East and Central Asia, and Europe for the next several centuries. The circular motion of the wheel was converted to a back and forth motion in the saw blade. Usually, only the saw was powered and the logs had to be loaded and transported manually. An early development was the development of a water-powered moving cart to move the billet steadily from the saw blade.

During the Industrial Revolution in the 18th century, the circular saw blade was invented and much more mechanization became possible with the development of steam power in the 19th century. Scrap lumber emerging from the mill provided a source of fuel to ignite the boiler. The arrival of the railways meant that logs were transported to the mills rather than the navigable waterways as well as the mills being built. By 1900, the world's largest sawmill was operated by the Atlantic Lumber Company in Georgetown, South Carolina, using floating logs from the Appalachian Mountains down the Pee Dee River. The introduction of electricity and high technology in the 20th century furthered this process, and now most sawmills are huge and expensive facilities where most aspects of the work are computerized. In addition to sawn timber, a variety of forestry products are offered using all by-products including sawdust, bark, sawdust and wood pellets.