Digital Book :
Hindu Goddesses: Visions of the Divine Feminine in the Hindu Religious Tradition.
By David R. Kinsley

Mahavidyas (Great Wisdoms) or Dasa Mahavidyas are a group of ten aspects of the Divine Mother or Devi in Hinduism. The Ten Mahavidyas are Wisdom Goddesses, who represent a spectrum of feminine divinity, from horrific goddesses at one end, to the ravishingly beautiful at the other [1].The development of Mahvidyas represents an important turning point in the history of Shaktism as it marks the rise of Bhakti aspect in Shaktism, which reached its zenith in 1700 CE. First sprung forth in the post-Puranic age, around 6th century C.E., it was a new theistic movement in which the supreme being was envisioned as female. A fact epitomized by texts like Devi-Bhagavata Purana, especially its last nine chapters (31-40) of the seventh skandha, which are known as the Devi Gita, and soon became central texts of Shaktism.

More at Wiki :
http://en.wikipedia.org/wiki/Mahavidya