↑ Nordhoff, Sebastian; Hammarström, Harald; Forkel, Robert; Haspelmath, Martin biên tập (2013). “Frisian”. Glottolog. Leipzig: Max Planck Institute for Evolutionary Anthropology.
↑ Gooskens, Charlotte (2004). “The Position of Frisian in the Germanic Language Area”. On the Boundaries of Phonology and Phonetics.
