The aims of this paper are to overview and examine the typological, cross-linguistic studies on the mood and modal systems, and to set up the Korean mood and modal systems. The summary of this paper is as follows. First, the modality can be defined to be the grammatical category which indicates the speaker's attitude toward the factuality and actualisation of the proposition. Second, the mood is realized into the inflectional form of the main verb and should carry distributional obligatoriness, and the other realm of modality is considered into the grammatical modality. Third, evidentials can be included into the realm of epistemic modality because they indirectly indicate the speaker's belief toward the proposition through marking the source of the information. Fourth, agent-oriented modality has a shortcoming since it is almost impossible to tell permission from permissives. Fifth, both epistemic modality and deontic modality can be characterized by the correspondence between the real world and the possible world, but the nature of the possible worlds and the direction of the fit differs. Sixth, deontic modality in Korean is realized into periphrastic constructions, and permission and obligation have a mirror image with regard to the scope of the negation. Seventh, irrealis mood can be defined as a scalar concept which includes the meaning of unreality, non-referring, low certainty. Eighth, the mood in Korean is realized into embedding endings such as ‘-um, -ki’, ‘-n, -l’. Ninth, the modality in Korean is realized into prefinal endings such as non-assertive ‘-keyss-, perceptionally evidential -te-’, and terminal endings ‘-kuna, -ney, -ci’. Tenth, ‘-ci’ indicates the speaker's attitude of knowing toward the proposition, and ‘-kuna, -ney’ indicate the speaker's attitude of newly perception toward the proposition.