Kim, Sook Young. 1996. Interface between root compounds and synthetic compounds. Studies in Modern Grammatical Theories 9: 205-228. The aim of this study is to reach the interface between root compounds and synthetic compounds using the theories of Roeper/Siegel(1978),Selkirk(1982) and Fabb(1984). A compound is a lexical unit consisting of more than one base word and functioning both grammatically and semantically as a single word. It can be divided into two classes: root compounds(or primary compounds)and synthetic compounds(or verbal compounds). Root compounds are those compounds whose second elements are not derivatives from verbs. On the other hand, synthetic compounds refer to those words which contain deverbal second constituents. Roeper/Siegel generally assume that both sentences and synthetic compounds are formed from subcategorization frames associated with verbs. They propose the First Sister Principle, which applies to the formation of synthetic compounds. Selkirk`s theory consists of two claims: (i) synthetic compoundings and root compoundings are generated by the same rewriting roles, (ii) the interpretation of a synthetic compounds is due to the optional rule for assigning grammatical functions to the nonhead element. Fabb regards -ing and -er case-markers, and specifies that they may be attached in syntax. The differences of the theories were found in the different explanations of phrases and non-heads with complements, etc. They show the interface between root compounds and synthetic compounds. In conclusion a distinctive syntactic explanation on the deverbal words, the second constituents of the compounds, may thus be the key to the understanding of the interface between root compounds and synthetic compounds.