This paper describes the first reported grammatical framework for a nmltimodal interface. Although multimodal interfaces offer the promise of a flexible and user fl'iendly means of human-coml)uter interaction, no study has yet appeared on formal granunatical f'l'ameworks for theln. We have developed MultiModal Definite Clause Ch'ammar (MM-I)CG), an extension of Definite Clause Gramumr. The major features of MM-I)CG inch, de eal)ability to handle an arbitrary mlmber of modes and temporal information in grammar rules, l:urther, we have developed MM-DCG translator to transfer rules in MM-DCG into Prolog predicates.