American pioneers, were European Americans, African Americans, Hispanic/Latino Americans, and Asian Americans, who settled the Western United States. The majority of the European-American and African-American settlers had marched west from the British Thirteen Colonies and later the United States of America, to settle and develop areas of the nation within the continent of North America. Others migrated north from Latin America and east from Asia.

The pioneer concept and ethos greatly predate the settlement of the Western United States, with which they are commonly associated, and many places now considered "East" were settled by pioneers from even further east. For example, Daniel Boone, a key figure in U.S. history, settled in Kentucky, when that "Dark and Bloody Ground" was still undeveloped.

One important development in the Western settlement were the Homestead Acts, which provided formal legislation for settlers which regulated the settlement process with little to no concern for the existing inhabitants of the land. Pioneers also settled on land that was once inhabited by American Indian tribes.

The word "pioneer" originates with the Middle French pionnier (originally, a foot soldier, or soldier involved in digging trenches), from the same root as peon or pawn. In the English language, the term independently evolved a sense of being an innovator or trailblazer. As early as 1664, Englishman John Evelyn used the term with a self-effacing "workman" meaning when he wrote in his treatise on planting, Sylva, or A Discourse of Forest-Trees: "I speak now in relation to the Royal Society, not my self, who am but a Servant of it only and a Pioneer in the Works".

Various figures in American folklore and literature typify the pioneer. James Fenimore Cooper's The Deerslayer (1841) became the most successful of his early series, the Leatherstocking Tales, about pioneer life in the Province of New York. Laura Ingalls Wilder's Little House on the Prairie series, published a century later from 1932 to 1943 but set sixty years prior, typified later depictions of pioneer families. Daniel Boone (1734–1820) and Davy Crockett (1786–1836) became two real-life icons of pioneer history.

The first westward migrations occurred as members of the Thirteen Colonies sought to expand their respective colonies westward. Those whose original royal charters did not specify a western limit simply extended their lands westward indefinitely.

After the United States was officially formed upon the ratification of the U.S. Constitution, federal coordination and legislation began to give settlement a more unified approach.

The Land Ordinance of 1785 was the first official action by the federal government in deciding how political organization of new territories would be handled. Then in 1787 the Northwest Ordinance declared that states could not individually claim new lands, and that westward expansion would be handled by the federal government. In implementing the Land Act of 1804, the government took its first steps towards legislating the manner in which land would be individually claimed by and distributed to settlers.