The Database of Old Icelandic Inflections (DOII) is a project at The Árni Magnússon Institute for Icelandic Studies (SÁM) at the University of Iceland with the goal to describe the inflectional patterns of Old Icelandic. DOII uses the same structure as the Database of Icelandic Morphology (DIM), which is an already developed digital resource. The linguistic data comes from A Dictionary of Old Norse Prose (ONP), a historical dictionary of the medieval language of Iceland and Norway. The first phase of the project focuses on simplex nouns. ONP lists over 2,400 simplex nouns with more than 10 citations, which give a broad representation of the noun system and can be processed in the DOII as an initial step to describe the inflectional patterns of Old Icelandic.