Íslendingabók (Icelandic pronunciation: [ˈistlɛntɪŋkaˌpouk], Book of Icelanders; Latin: Libellus Islandorum) is a historical work dealing with early Icelandic history. The author was an Icelandic priest, Ari Þorgilsson, working in the early 12th century. The work originally existed in two different versions but only the younger one has come down to us. The older contained information on Norwegian kings, made use of by later writers of kings' sagas.
The priest Jón Erlendsson in Villingaholt (died 1672) in the service of bishop Brynjólfur Sveinsson made two copies of Íslendingabók (now AM 113 a fol and AM 113 b fol at the Árni Magnússon Institute for Icelandic Studies), the latter one because the bishop was unhappy with the first version. The original copied from is assumed to have dated to ca. 1200. It was lost in the course of the late 17th century, and when Árni Magnússon looked for it, it had disappeared without a trace.
Íslendingabók is a concise work which relates the major events of Icelandic history in terse prose. While the author is forced to rely almost exclusively on oral history he takes pains to establish the reliability of his sources and mentions several of them by name. He avoids supernatural material and Christian bias. The prologue of the book explicitly states that whatever might be wrong in the account must be corrected to "that which can be proven to be most true". Due to these qualities of the work and the early time of its writing, historians consider it the most reliable extant source on early Icelandic history.
Íslendingabók (Icelandic pronunciation: [ˈistlɛntɪŋkaˌpouk], literally 'book of Icelanders') is a database created by the biotechnology company deCODE genetics, attempting to record the genealogy of all Icelanders who have ever lived, insofar as sources are available; a total of approximately 810,000 people are recorded. The database is likely to contain information on about half of all Icelanders who have lived in Iceland since its settlement. It is part of a wider scheme that has been characterised as 'one of the first, and to date most contentious' attempts to assemble a large genetic database.
Íslendingabók gets its name from the first history of Iceland, by Ari the Wise; the choice of name, and the project as a whole, has been interpreted as a public-relations excerise by deCODE, appealing to Icelandic public nationalist sentiments.
Interest in genealogy in Iceland is strong, with the Icelandic Ættfræðifélagið (Genealogical Society) founded in 1945; shortly before, Halldór Laxness had proposed a similar gathering of information to that manifested in Íslendingabók today; Friðrik Skúlason of FRISK Software International began constructing a genealogical database of Icelanders in the 1990s, successfully developing and marketing genealogical software (called Espólín).