This study discusses topic and focus constructions in spoken Korean within the framework of information structure. Information structure is a part of grammar that deals with the relation between linguistic forms and the mental states of speakers and hearers. Since the different formal realizations of topic and focus constructions in Korean are due to differences in speakers’ assumptions about the mental states of hearers, research on Korean topic and focus constructions falls under the proper domain of information structure.

Five different topic constructions in Korean are reviewed and their discourse contexts are analyzed; zero pronouns, bare NPs, and right-dislocated NPs are generally used for discourse-active topic referents, and the maliya -construction and nun-marked NPs are generally used for topic referents that are not discourse-active. Sometimes, active topic referents are also marked with –nun when the topic referents have more salient topics already established in the discourse or speakers are considering potential alternatives to the active topic referents. Topics are divided into ratified and unratified topics according to whether their status as topics is assumed to be taken for granted by hearers. Among the five topic constructions in Korean, zero pronouns, bare NPs and right-dislocated NPs express ratified topics, while the maliya-construction and nun-marked topics express unratified topics.

The marker –ka, which has been long regarded as a subject indicator, is reanalyzed, and it is suggested that – ka marks not only the subject but also argument focus and sentence focus. Accessible or active referents can sometimes be marked with – ka, constituting sentence-focus constructions. In those constructions, the propositional content of the sentences expresses some unexpected or surprising event. Also, frequent occurrences of the maker –ka in presupposed subordinate clauses are examined, and it is suggested that –ka can be used as a mere subject indicator, losing its function of indicating focus in presupposed clauses with topic-comment construals, in which there is no actual focus.