Phi Alpha Theta (ΦΑΘ) is an American honor society for undergraduate and graduate students and professors of history. The society has over 350,000 members, with about 9,500 new members joining each year through 860 local chapters.

Phi Alpha Theta was established on March 17, 1921 at the University of Arkansas by Professor Nels Cleven. Cleven had become convinced in his time at the university that a fraternity of scholars (which would accept men or women) was important for the study of history. He invited students to a meeting to form the society (then called the “University Historical Society”) on March 14, and the society was officially recognized on the 17th. In April, the decision was made for the society to be known by the Greek letters Phi Alpha Theta.