* "Undersøgelse om det gamle Nordiske Sprogs Oprindelse" (1811) - This is Rask's dissertation which explored the origins of Old Norse, laying the foundation for his later work on comparative linguistics.
* "Vejledning til det islandske Sprog" (1811) - This was a textbook on the Icelandic language, which helped popularize the study of this important Scandinavian language.
* "Anvisning til det islandske Sprog" (1818) - This was an updated and revised version of the earlier Icelandic textbook.
* "Undersøgelse om det gamle Nordiske Sprogs grammatiske Bygning" (1818) - This book discussed the grammatical structure of Old Norse, further developing his comparative linguistic methods.
* "Om Sprogenes Oprindelse" (1822) - In this work, Rask proposed his theory of the origin of languages, which differed significantly from the theories of his contemporaries.
* "Angelsaksisk Sproglære" (1827) - This was a textbook on Old English, demonstrating his wide-ranging interests in Germanic languages.
* "Danish Grammar" (1830) - This was a grammar of the Danish language, showcasing his mastery of his native tongue.
These are just some of the key works by Rasmus Rask. He also wrote numerous articles and essays on various topics related to linguistics and philology. His contributions significantly advanced the field of comparative linguistics, particularly his analysis of Indo-European languages.