Martha Louise Root (August 10, 1872 – September 28, 1939) was an American traveling teacher of the Bahá'í Faith in the early 20th century.
From the declaration of her belief in 1909 until her death thirty years later, she went around the world four times.
Shoghi Effendi, then head of the Bahá'í Faith, called her "the foremost travel teacher in the first Bahá'í Century", and named her a Hand of the Cause posthumously.
Known by her numerous visits with Heads of State and other public figures, of special importance was her efforts with Queen Marie of Romania, considered the first royal to accept Bahá'u'lláh.