Auxiliary verbs in Icelandic grammar, also known as “háttarmerki”, are verbs that help to convey the various moods, voices, aspects and tenses of other verbs. They play a critical role in structuring sentences and expressing accurate meaning. Some common Icelandic auxiliary verbs include “vera” (be), “hafa” (have), “geta” (can), “munu” (will), “skulu” (shall), and “vilja” (want). These verbs are essential for understanding and correctly using the Icelandic language.