Epistolary novel

An epistolary novel is a novel written as a series of documents. The usual form is letters, although diary entries, newspaper clippings and other documents are sometimes used. Recently, electronic "documents" such as recordings and radio, blogs, and e-mails have also come into use. The word epistolary is derived through Latin from the Greek word ἐπιστολή epistolē, meaning a letter (see epistle).The epistolary form can add greater realism to a story, because it mimics the workings of real life. It is thus able to demonstrate differing points of view without recourse to the device of an omniscient narrator.

http://en.wikipedia.org/wiki/Epistolary_novel