The language of the First Riustring Manuscript, dating from ca. 1300 AD, represents the most archaic stage of Old Frisian. The mainly legal texts are famous for their historical value. However, a grammatical treatise of this important codex is still lacking. This book is meant to meet this need. It contains an inventory of the linguistic evidence as well as a synchronic study of the grammar. Moreover, historical linguistic problems are discussed wherever relevant. The book is intended for all students of Old Frisian, not just linguists but also legal historians, philologists, historians, and others.