Multimodal dialogue systems are interactive systems which support
several modes of communication with the user, for example speech,
mouse clicks and drawings. We present a method for writing multimodal
grammars in the Grammatical Framework (GF) and for using such grammars
in dialogue systems. Parallel multimodality, where the same
information is represented in multiple modalities, is achieved by
using multiple concrete syntaxes for the same abstract
syntax. Integrated multimodality, where the different modalities are
used together to represent some information, is done by using record
types. We will also present an example multimodal dialogue system
implemented using these techniques. This work is part of the TALK
project (http://www.talk-project.org/).