This article discusses some vowel deletion rules in various stages of Icelandic. These rules are operative when a vowel-initial ending is added to a vowel-final stem. In Old Icelandic, a was dropped after á; u was dropped after á, ó and ú; and i was dropped after é. These rules have been subject to various changes, some of which can be attributed to changes in the phonology, but others are due to analogy. As a result, the deletion rules can not be stated as general phonological rules in Modern Icelandic; they must refer to grammatical features such as part of speech, gender etc. The author shows how these rules have gradually changed from Old to Modern Icelandic.