A: The roots of New Thought can be traced even further back in history. The Greek/Jewish Bible philosopher Philo (20 BCE - 50 CE) believed that God was too complex and marvelous to be understood in literal human terms, and therefore we should not embrace a literal interpretation of the Bible. Origen (184-253 CE), one of early Christianity's theologians believed in Universalism, the idea that everyone is already reconciled with God. Meister Eckhart (1260-1327 CE), the German theologian and mystic and Dominican Friar, said that "God is the innermost part of each and every thing."
The term "New Thought" refers to the movements and philosophy that emerged from the healing ministry of Mary Baker Eddy in the latter part of the 1800's. Although there are some variations between the movements (Unity, Religious Science, Divine Science), the basic philosophy is the same: God/Spirit is everywhere is the totality of real things, true human selfhood is divine, Divine thought is a force for good, sickness originates in the mind, and "right thinking" has a healing effect [Wikipedia].
Mary Baker Eddy was the founder of Christian Science. She published the influential Science and Health in 1875. In 1881 she founded the Massachusetts Metaphysical College, and in 1908 she started The Christian Science Monitor, a Pulitzer Prize winning newspaper still in circulation (and online). One of her students, Emma Curtis Hopkins, would go on to teach some of the founders of New Thought movements we know today, such as Charles and Myrtle Fillmore (Unity), Ernest Holmes (Religious Science), and Malinda Cramer (Divine Science).
The video below gives an overview of Mary Baker Eddy's life and work.Click here for a historical look at Unity.