One of the most interesting changes in Proto-Germanic was the alternation of "y" and "w" after short syllables with "i" and "u" after long, respectively - an alternation with far-reaching effects. Described by Eduard Sievers in 1878, this -law- has been the subject of controversy ever since. Is it related to a similar phenomenon in Vedic Sanskrit, and was it, therefore, Indo-European in origin? What is its relationship to alliterative verse in Germanic? This study addresses such questions and demonstrates that Sievers' Law has played a wider role in Old English than heretofore demonstrated."