The Harmony Society was a Christian theosophy and pietist society founded in Iptingen, Germany, in 1785. Due to religious persecution by the Lutheran Church and the government in Württemberg, the group moved to the United States, where representatives initially purchased land in Butler County, Pennsylvania. On February 15, 1805, the group of approximately 400 followers formally organized the Harmony Society, placing all their goods in common.

Under its founder and spiritual leader, Johann Georg Rapp (1757–1847); Frederick (Reichert) Rapp (1775–1834), his adopted son who managed its business affairs; and their associates, the Society existed for one hundred years, roughly from 1805 until 1905. Members were known as Harmonists, Harmonites, or Rappites. The Society is best known for its worldly successes, most notably the establishment of three model communities, the first at Harmony, Pennsylvania; the second, also called Harmony, in the Indiana Territory, now New Harmony, Indiana; and the third and final town at Economy, now Ambridge, Pennsylvania.