At his death in 1959, Felix Jacoby left to posterity a monumental work assembling the fragments of more than 870 Greek historians. Yet the sheer bulk of the material and the lack of transparency of the plan make the Fragmente der Griechischen Historiker difficult to use and it is often avoided by students. The three indexes now published are the first fruits of an indexation project which aims to facilitate access to the corpus of fragments and to improve its usefulness. Index no. 1 places all sources of fragments in a list alphabetized by author and work, index no. 2 follows the order of presentation found in Jacoby, while index no. 3 places the authors of fragments in alphabetical order and gives under each one an alphabetized list of authors who cite him.The practical advantages are clear. Index no. 1 allows the reader to find his way from a fragment he has come across in his reading to the entry in Jacoby: he can then situate it within the lost work and note Jacoby's comment on it. Index no. 3 offers a complete resolution of Jacoby's abbreviations, which are often obscure and sometimes inconsistent. It also returns to their right place the often overlooked fragmenta and testimonia given by Jacoby in the addenda. In general, the indexes make it a simple matter to ascertain which historians had read (or not read) the works, now lost, of their predecessors, thus throwing light on the contents of libraries as well as the transmission of historical texts and their lifespan.