First established in 1790, American prison libraries were instituted as a method for reforming behavior, usually through religious means. Clergy often ran the prisons, and early libraries usually contained only scriptural texts. While libraries grew to include secular materials, it wasn't until 1977 that the U.S. government acknowledged a constitutional responsibility to provide inmates access to a law library to ensure access to information that would help them litigate their own appeals and empower themselves. However, a subsequent ruling complicated the mandate for law libraries in all prisons. Now, inmates are required to prove their rights are impinged by inadequate access to legal materials for a full library to be provided, in some cases.
Source : http://wcfcourier.com/news/national/editorial-roundup-excerpts-from-recent-editorials/article_5b3082de-27b7-5cfc-9f28-8533bd6a93a4.html