The Organization of American Historians (OAH), formerly known as the Mississippi Valley Historical Association, is the largest professional society dedicated to the teaching and study of American history. OAH's members in the U.S. and abroad include college and university professors; historians, students; precollegiate teachers; archivists, museum curators, and other public historians; and a variety of scholars employed in government and the private sector. The OAH publishes the Journal of American History. Among its various programs, OAH conducts an annual meeting each spring, and has a robust roster on its OAH Distinguished Lecturership Program.

The organization's mission is to promote excellence in the scholarship, teaching, and presentation of American history, and encourage wide discussion of historical questions and equitable treatment of all practitioners of history. Membership is open to all who wish to support its mission.

In 2010 its individual membership is approximately 8,000 and its institutional membership approximately 1,250. For its 2009 fiscal year ending June 30, 2009, the organization's operating budget was approximately $2.9 million.