Farmall was a model name and later a brand name for tractors manufactured by International Harvester (IH), an American truck, tractor, and construction equipment company. The Farmall name was usually presented as McCormick-Deering Farmall and later McCormick Farmall in the evolving brand architecture of IH.

Farmall was a prominent brand in the 20th-century trend toward the mechanization of agriculture in the US. Its general-purpose machines' origins were in row-crop tractors, a category that they helped establish and in which they long held a large market share. During the decades of Farmall production (1920s to 1980s), most Farmalls were built for row-crop work, but many orchard, fairway, and other variants were also built. Most Farmalls were all-purpose tractors that were affordable for small to medium-sized family farms, and could do enough of the tasks needed on the farm that the need for hired hands was reduced and for working horses or mules eliminated.

The original Farmall is widely viewed as the first tractor to combine a set of traits that would define the row-crop tractor category, although competition in the category came quickly. Although it was not the first tractor to have any one of these traits, it was early in bringing the winning combination to market. The traits included (a) 'tricycle' configuration (a single front wheel or narrowly spaced pair), high ground clearance, quickly adjustable axle track, excellent visibility all around and under the machine, and light weight; (b) sufficient power for plowing and harrowing, and a belt pulley for belt work; and (c) all at low cost, with a familiar brand and an extensive distribution and service network. The first group of traits allowed for more nimble maneuvering and accurate cultivation than most other tractors of the day; additionally, because of the second group, the Farmall could also, like previous tractors, perform all the other duties a farmer would have previously achieved using a team of horses. A tractor could yield lower overall operating costs than horses as long as it was priced right and reliable (and its fuel supply as well). The Farmall, mass-produced with the same low-cost-and-high-value ethos as the Ford Model T or Fordson tractor, could meet that requirement. The Farmall was thus similar to a Fordson in its capabilities and affordability, but with better cultivating ability.

Descriptions of tractors as "general-purpose" and "all-purpose" had been used loosely and interchangeably in the teens and early twenties; but a true all-purpose tractor would be one that not only brought power to plowing, harrowing, and belt work but also obviated the horse team entirely. This latter step is what changed the financial picture to heavily favor the mechanization of agriculture. The Farmall was so successful at total horse replacement that it became a strong-selling product. With the success of the Farmall line, other manufacturers soon introduced similar general- to all-purpose tractors with varying success.

In later decades, the Farmall line continued to be a leading brand of all-purpose tractors. Its bright red color was a distinctive badge. During the 1940s and 1950s, the brand was ubiquitous in North American farming. Various trends in farming after the 1960s—such as the decline of cultivating in favor of herbicidal weed control, and the consolidation of the agricultural sector into larger but fewer farms—ended the era of Farmall manufacturing. However, many Farmalls remain in farming service, and many others are restored and collected by enthusiasts. In these respects, the Farmall era continues. As predicted in the 1980s and 1990s, the growing public understanding of environmental protection, and of sustainability in general, have brought a corollary resurgence of interest in organic farming and local food production. This cultural development has brought a limited but notable revival of cultivating and of the use of equipment such as Farmalls.

Being an amalgamation, IH, like General Motors, gradually evolved a brand architecture during the first half of the 20th century, when the concept was still new. IH capitalized on farmers' familiarity with its older brands stretching back to individual entrepreneurs of the earliest days of agricultural mechanization (Cyrus McCormick, William Deering), which is why legacy company brands McCormick and Deering were used. The Farmall name itself began as a model name and then evolved to encompass a model line. With the success of the Farmall, other manufacturers soon introduced similar general- to all-purpose tractors with varying success. In their early years, they often included the word "all" in the name of the product. During the first decade of Farmall sales, IH's advertising even had to emphasize the name's correlation to IH, to protect the brand name from genericization. The shift to a bright, distinctive color scheme in 1936 helped to further strengthen the branding effort.

The Fordson was the first truly mass-produced, light, affordable tractor, and thus the first to tap the market of small to medium family farms on a large scale. Its design was excellent in many respects, including design for manufacturability and the low cost that it allowed. But one task that its design had not been tailored to was cultivating the rows of young row-crop plants to kill the weeds. IH recognized motorized cultivating as an unmet need in the marketplace. It was also under intense competitive pressure to build a "Fordson beater" soon, lest the Fordson go on to dominate the entire marketplace of agricultural equipment, imperfections or no.

IH's first effort to solve this problem was a motor cultivator, a class of machine that various companies were building and selling in the late 1910s and early 1920s. As the name implies, these were self-propelled cultivators in the simplest sense—little more than a horse implement with a motor added. The IH motor cultivator and another all-purpose tractor, the Moline Plow Company's Universal, both sold several hundred units in the late 1910s. IH's machine was not particularly successful; the Moline Universal was more successful, but its parent company nevertheless faced dire financial straits. Both models were soon discontinued. Many farmers were content (and could afford) to keep one or two horses or mules around to do miscellaneous light work (such as cultivating).