Möðruvallabók (AM 132 fol.) — a mid-14th-century Icelandic vellum codex, the largest surviving medieval collection of Sagas of Icelanders and the principal manuscript for most of the sagas it contains.

The original portion is written in a single hand and runs to 189 vellum leaves in double columns, with eleven 17th-century paper leaves supplied at the front to replace the lost opening of Njáls saga.

The eleven sagas stand in the order Njáls saga, Egils saga Skallagrímssonar, Finnboga saga ramma, Bandamanna saga, Kormáks saga, Víga-Glúms saga, Droplaugarsona saga, Ölkofra þáttr, Hallfreðar saga, Laxdæla saga and Fóstbræðra saga.

Arinbjarnarkviða is copied after Egils saga and survives nowhere else, though water damage has left much of it illegible. A note after Njáls saga indicates Gauks saga Trandilssonar was meant to follow but was never entered; that saga is now lost.

The manuscript takes its name from Möðruvellir in Eyjafjörður, where Magnús Björnsson signed it in 1628; it was brought to Denmark by his son in 1684, entered the Arnamagnæan Collection, and was returned to Iceland in 1974.