In Korean linguistics, the study of auxiliary verbs, beginning with Chhve Hyon Be's study of traditional grammar in the 30s of the 20th century, is still the object of continuous research. This article focuses on the auxiliary verbs in Korean linguistics and the criteria for their differentiation. It examines the subordinate verbs' attachment to the leading verb, and the auxiliary verbs add meaning to the leading verb. The properties of auxiliary verbs are semantically and syntactically dependent on the leading verb, and have aspect and modal meanings. It also clarifies the relation of auxiliary verbs with related forms and the use of similar verbs together with the main verbs.