Baird, Joseph L and Ehrman, Radd K. The Letters of Hildegard of Bingen. (Oxford University Press, 2004).
Flanagan, Sabina. Hildegard of Bingen: A Visionary Life. (London: Routledge, 1998).
Wilson, Katharina. Medieval Women Writers. (Athens, GA: University of Georgia Press, 1984).
The Life and Works of Hildegard von Bingen: http://www.fordham.edu/halsall/med/hildegarde.asp