The Old Frisian Etymological Dictionary is an indispensable research tool for the study of Old Frisian, Germanic languages, and Proto-Indo- European. With this first etymological dictionary of Old Frisian based on the lexicon of Riustring 1 manuscript, Old Frisian becomes accessible to a wide circle of scholars of Germanic and Indo-European. The latest insights of Comparative Indo-European Linguistics have been systematically incorporated. The entries are provided with a meticulous analysis of Old Frisian dialectal forms, with Proto-Frisian reconstructions, and with a wealth of Germanic and Indo- European cognates. Due to the lack of lexicographical tools, Old Frisian cognates are rarely included in current etymological dictionaries of Germanic and Indo-European, despite the fact that Old Frisian can often provide important clues for the reconstruction. At the same time, it is difficult for the students of Old Frisian to acquire knowledge of the linguistic prehistory of this language. The Old Frisian Etymological Dictionary is an indispensable research tool for the study of Old Frisian, Germanic languages, and Proto-Indo-European.