Peanut butter is a food paste or spread made from ground, dry-roasted peanuts. It commonly contains additional ingredients that modify the taste or texture, such as salt, sweeteners, or emulsifiers. Consumed in many countries, it is the most commonly used of the nut butters, a group that also includes cashew butter and almond butter.

Peanut butter is a nutrient-rich food containing high levels of protein, several vitamins, and dietary minerals. It is typically served as a spread on bread, toast, or crackers and used to make sandwiches (notably the peanut butter and jelly sandwich). It is also used in a number of breakfast dishes and desserts, such as granola, smoothies, crepes, cookies, brownies, or croissants.

The earliest references to peanut butter can be traced to Aztec and Inca civilizations, who ground roasted peanuts into a paste. The Bainbridge Post-Searchlight reports that 16th-century Aztecs used peanut paste for aching gums.

Several people can be credited with the invention of modern peanut butter and the processes involved in making it. The U.S. National Peanut Board credits three modern inventors with the earliest patents related to the production of modern peanut butter. Marcellus Gilmore Edson of Montreal, Quebec, Canada, obtained the first patent for a method of producing peanut butter from roasted peanuts using heated surfaces in 1884. Edson's cooled product had "a consistency like that of butter, lard, or ointment" according to his patent application which described a process of milling roasted peanuts until the peanuts reached "a fluid or semi-fluid state". He mixed sugar into the paste to harden its consistency.

A businessman from St. Louis named George Bayle produced and sold peanut butter in the form of a snack food in 1894. By 1917, American consumers used peanut products during periods of meat rationing, with government promotions of "meatless Mondays" when peanut butter was a favored choice.

John Harvey Kellogg, known for his line of prepared breakfast cereals, was an advocate of using plant foods as a healthier dietary choice than meat. He was issued a patent for a "Process of Producing Alimentary Products" on May 24, 1898, and used peanuts, although he boiled the peanuts rather than roasting them. Kellogg's Western Health Reform Institute served peanut butter to patients because they needed a food that contained a large amount of protein that could be eaten without chewing. At first, peanut butter was a food for wealthy people, as it became popular initially as a product served at expensive health care institutes.

Although often credited as its inventor, George Washington Carver did not invent peanut butter. By the time Carver published his document about peanuts, entitled "How to Grow the Peanut and 105 Ways of Preparing it For Human Consumption" in 1916, many methods of preparation of peanut butter had already been developed or patented by various pharmacists, doctors, and food scientists working in the US and Canada.

Early peanut-butter-making machines were developed by Joseph Lambert, who had worked at Kellogg's Battle Creek Sanitarium, and Dr. Ambrose Straub who obtained a patent for a peanut-butter-making machine in 1903.